Multi-carrier frequency-division multiplexing (FDM) architecture for high speed digital service in local networks

ABSTRACT

Disclosed herein are methods of providing a client with local area network connectivity and access to other services in a cable network. One such method includes: allocating bandwidth in the network to support bi-directional data communication between the host and a central concentrator. Bandwidth is allocated for a downstream flow on at least one downstream frequency channel based on a mapping between the downstream flow and a particular octet in a downstream packet. Bandwidth is allocated for an upstream flow on at least one non-shared upstream tone. The method also includes conveying a bi-directional data flow between the host and the concentrator over the allocated bandwidth, including conveying the upstream flow using the allocated bandwidth and conveying the downstream flow using the allocated bandwidth. The method also includes utilizing bandwidth in the network not allocated to data communications to provide the host with at least one audio/visual service.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This present application claims priority to copending U.S. provisionalapplication having Ser. No. 60/322,966, which was filed on Sep. 18, 2001and is entirely incorporated herein by reference. Also, this presentapplication claims priority to copending U.S. provisional applicationhaving Ser. No. 60/338,868, which was filed on Nov. 13, 2001 and isentirely incorporated herein by reference. In addition, this presentapplication claims priority to copending U.S. provisional applicationhaving Ser. No. 60/342,627, which was filed on Dec. 20, 2001 and isentirely incorporated herein by reference. Moreover, this presentapplication claims priority to copending U.S. provisional applicationhaving Ser. No. 60/397,987, which was filed on Jul. 23, 2002, and isentirely incorporated herein by reference.

Furthermore, the present application is related to U.S. patentapplication ser. No. 10/245,054, filed Sep. 17, 2002; U.S. patentapplication Ser. No. 10/245,250, filed Sep. 17, 2002; U.S. patentapplication Ser. No. 10/244,899, filed Sep. 17, 2002; U.S. patentapplication Ser. No. 10/245,179, filed Sep. 17, 2002; U.S. patentapplication Ser. No. 10/245,853, filed Sep. 17, 2002; and U.S. patentapplication Ser. No. 10/245,032, filed Sep. 17, 2002, U.S. patentapplication Ser. No. 10/245,853 is entirely incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to the field of communicationnetworks and systems for using frequency-division multiplexing to carrydata across broadband networks with the potential to support a pluralityof subscribers at high data rates.

BACKGROUND OF THE INVENTION

Many solutions have been tried for delivering digital data services tocustomers over cable networks. Historically, cable networks weredesigned for community antenna television (CATV) delivery supporting 6MHz analog channels that were frequency-division multiplexed into aradio-frequency (RF) medium that was primarily coaxial cable or coax. Tosupport higher throughput and advanced digital services, many of thesecable TV networks migrated to a hybrid fiber-coax (HFC) architecture.With the development of HFC networks to support advanced services, suchas digital television channels, the capability to provide bi-directionaldata services also evolved.

At present bi-directional data services are often available to customersusing systems based upon the DOCSIS (Data-Over-Cable Service InterfaceSpecifications) industry standards promulgated by Cable TelevisionLaboratories or CableLabs. The DOCSIS standards comprise many documentsthat specify mechanisms and protocols for carrying digital data betweena cable modem (CM), generally located at a customer premises, and acable modem termination system (CMTS), commonly located within theheadend of the service provider. Within distribution networks in thecable industry, data flowing from a service provider to a customerpremises is commonly referred to as downstream traffic, while dataflowing from a customer premises to a service provider is generallyknown as upstream traffic. Although DOCSIS is a bridged architecturethat is capable of carrying other network protocols besides and/or inaddition to the Internet Protocol (IP), it is primarily designed andused for Internet access using IP.

Furthermore, for many cable system operators (also known as multiplesystem operators or MSOs) the primary market for selling services suchas cable TV, Internet access, and/or local phone services has beenresidential customers. Although DOCSIS cable modems could be used bybusiness customers, DOCSIS was primarily designed to meet the Internetaccess needs of residential users. To make the deployment of DOCSISsystems economically feasible, the DOCSIS standards were designed tosupport a large number of price-sensitive residential, Internet-accessusers on a single DOCSIS system. Though home users may desire extremelyhigh speed Internet access, generally they are unwilling to paysignificantly higher monthly fees. To handle this situation DOCSIS wasdesigned to share the bandwidth among a large number of users. Ingeneral, DOCSIS systems are deployed on HFC networks supporting manyCATV channels. In addition, the data bandwidth used for DOCSIS generallyis shared among multiple users using a time-division multiple-access(TDMA) process.

In the downstream direction the DOCSIS CMTS transmits to a plurality ofcable modems that may share at least one downstream frequency. In effectthe CMTS dynamically or statistically time-division multiplexesdownstream data for a plurality of cable modems. In general, based ondestination addresses the cable modems receive this traffic and forwardthe proper information to user PCs or hosts. In the upstream directionthe plurality of cable modems generally contend for access to transmitat a certain time on an upstream frequency. This contention for upstreamslots of time has the potential of causing collisions between theupstream transmissions of multiple cable modems. To resolve these andmany other problems resulting from multiple users sharing an upstreamfrequency channel to minimize costs for residential users, DOCSISimplements a media access control (MAC) algorithm. The DOCSIS layer 2MAC protocol is defined in the DOCSIS radio frequency interface (RFI)specifications, versions 1.0, 1.1, and/or 2.0. DOCSIS RFI 2.0 actuallyintroduces a code division multiple access (CDMA) physical layer thatmay be used instead of or in addition to the TDMA functionalitydescribed in DOCSIS RFI 1.0 and/or 1.1.

However, the design of DOCSIS to provide a large enough revenue streamby deploying systems shared by a large number of residential customershas some drawbacks. First, the DOCSIS MAC is generally asymmetric withrespect to bandwidth, with cable modems contending for upstreamtransmission and with the CMTS making downstream forwarding decisions.Also, though DOCSIS supports multiple frequency channels, it does nothave mechanisms to quickly and efficiently allocate additional frequencychannels to users in a dynamic frequency-division multiple access (FDMA)manner. Furthermore, while the data rates of DOCSIS are a vastimprovement over analog dial-up V.90 modems and Basic Rate Interface(BRI) ISDN (integrated services digital network) lines, the speeds ofDOCSIS cable modems are not significantly better than other serviceswhich are targeted at business users.

Because businesses generally place high value on the daily use ofnetworking technologies, these commercial customers often are willing topay higher fees in exchange for faster data services than are availablethrough DOCSIS. The data service needs of businesses might be met byusing all-fiber optic networks with their large bandwidth potential.However, in many cases fiber optic lines are not readily availablebetween business locations. Often new installations of fiber opticlines, though technically feasible, are cost prohibitive based onfactors such as having to dig up the street to place the lines. Also, inmany cases the devices used in optical transmission (including, but notlimited to, fiber optic lines) are relatively newer than the devicesused in electrical transmission (including, but not limited to coaxcable transmission lines). (Both electrical and optical transmissionsystems may use constrained media such as, but not limited to,electrical conductors, waveguides, and/or fiber as well as unconstrainedmedia in wireless and/or free-space transmission.) As a result,generally more development time has been invested in simplifying andreducing the costs of devices used in electrical communication systems,such as but not limited to coax CATV systems, than the development timethat has been invested in devices used in optical communication systems.Thus, although fiber optics certainly has the capability of offeringhigh data rates, these issues tend to drive up the costs of fiber opticcommunication systems.

Furthermore, in deploying networks to support primarily residentialaccess, the transmission lines of the MSOs generally run past manybusinesses. Thus, a technical solution that functions over existing HFCnetworks of the MSOs, that provides higher data rates than DOCSIS, andthat has the capability of working in the future over all fiber networksis a distinct improvement over the prior art and has the capability ofmeeting the needs of a previously untapped market segment.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the present invention. Moreover, in the drawings, like referencenumerals designate corresponding parts throughout the several views. Thereference numbers in the drawings have at least three digits with thetwo rightmost digits being reference numbers within a figure. The digitsto the left of those two digits are the number of the figure in whichthe item identified by the reference number first appears. For example,an item with reference number 211 first appears in FIG. 2.

FIG. 1 shows a block diagram of central and remote transceiversconnected to a cable transmission network.

FIG. 2 a shows a block diagram of a transport modem termination systemconnected to a cable transmission network.

FIG. 2 b shows a block diagram of a plurality of client transport modemsconnected to a cable transmission network.

FIG. 3 shows a block diagram of the connection-oriented relationshipbetween client transport modems and ports of a transport modemtermination system.

FIG. 4 shows a block diagram of the architecture for integrating atransport modem termination system and a plurality of client transportmodems into a system carrying other services.

FIG. 5 a shows a block diagram of a transport modem termination systemconnected in a headend.

FIG. 5 b shows a block diagram of a client transport modem connected toa cable transmission network.

FIG. 6 shows a block diagram of some protocols that may be used in thesystem control of a transport modem termination system (TMTS) and/or aclient transport modem (cTM).

FIG. 7 shows a block diagram of a TMTS and a cTM providing physicallayer repeater service.

FIG. 8 shows an expanded block diagram of the protocol sublayers withinthe physical layer of the TMTS and the cTM.

FIG. 9 shows how a cable transmission physical layer fits in the OSImodel.

FIG. 10 shows a cable transmission physical layer that is part of anetwork interface card.

FIG. 11 shows an expansion of the cable transmission physical layerexpanded into four sublayers in a network interface card.

FIG. 12 shows a reference diagram of the downstream and upstreamfunctions of the four sublayers.

FIG. 13 shows the relationship among 802.3/ethernet media, the framemanagement sublayer, and the inverse multiplex sublayer.

FIG. 14 shows the IEEE 802.3/ethernet frame format.

FIG. 15 shows the control frame format.

FIG. 16 shows the frame management sublayer (FMS) frame format.

FIG. 17 shows the relationship among the frame management sublayer(FMS), the inverse multiplex sublayer (IMS), and the physical codingsublayer (PCS).

FIG. 18 shows the MPEG frame format.

FIG. 19 shows the MPEG adaptation field format.

FIG. 20 shows clock distribution from a TMTS to a cTM.

FIG. 21 shows a clock timing diagram for the TMTS and the cTM.

FIG. 22 shows the downstream inverse multiplex sublayer (IMS)communication of MPEG packets over multiple carriers.

FIG. 23 shows the TMTS downstream IMS sublayer.

FIG. 24 shows the formation of MPEG packets from FMS frames.

DETAILED DESCRIPTION

In general, the seven-layer Open Systems Interconnect (OSI) model is auseful abstraction in analyzing and describing communication protocolsand/or systems. The seven layers of the OSI model from lowest to highestare: 1) the physical layer, 2) the data link layer, 3) the networklayer, 4) the transport layer, 5) the session layer, 6) the presentationlayer, and 7) the application layer. This OSI model is well-known tothose of ordinary skill in the art. Furthermore, the OSI model layershave often been broken down into sub-layers in various contexts. Forexample, the level two, data link layer may be divided into a mediumaccess control (MAC) sublayer and a logical link control (LLC) sublayerin the documentation of the IEEE (Institute for Electrical andElectronic Engineers) standard 802. Furthermore, some of the IEEEstandards (such as for 100 Mbps fast ethernet and 1 Gbps gigabitethernet) break level one (i.e., the physical layer) down into sublayerssuch as, but not limited to, the physical coding sublayer (PCS), thephysical medium attachment layer (PMA), and the physical media dependent(PMD) sublayer. These sublayers are described more fully in the IEEE 802specifications and more specifically in the IEEE 802.3/ethernetspecifications. The specifications of IEEE 802 (including, but notlimited to, IEEE 802.3) are incorporated by reference in their entiretyherein.

In general, the preferred embodiments of the present invention comprisephysical layer protocols that may be implemented in physical layertransceivers. The physical layer interfaces and/or protocols of thepreferred embodiments of the present invention may be incorporated intoother networking methods, devices, and/or systems to provide varioustypes of additional functionality. Often the behavior and capabilitiesof networking devices are categorized based on the level of the OSImodel at which the networking device operates.

Repeater, bridge, switch, router, and gateway are some commonly usedterms for interconnection devices in networks. Though these terms arecommonly used in networking their definition does vary from context tocontext, especially with respect to the term switch. However, a briefdescription of some of the terms generally associated with various typesof networking devices may be useful. Repeaters generally operate at thephysical layer of the OSI model. In general, digital repeaters interpretincoming digital signals and generate outgoing digital signals based onthe interpreted incoming signals. Basically, repeaters act to repeat thesignals and generally do not make many decisions as to which signals toforward. As a non-limiting example, most ethernet hubs are repeaterdevices. Hubs in some contexts are called layer one switches. Incontrast to repeaters, bridges and/or layer-two switches generallyoperate at layer two of the OSI model and evaluate the data link layeror MAC layer (or sublayer) addresses in incoming frames. Bridges and/orlayer two switches generally only forward frames that have destinationaddresses that are across the bridge. Basically, bridges or layer twoswitches generally are connected between two shared contention mediausing media access control (MAC) algorithms. In general, a bridge orlayer two switch performs an instance of a MAC algorithm for each of itsinterfaces. In this way, bridges and/or layer two switches generally maybe used to break shared or contention media into smaller collisiondomains.

Routers (and layer three switches) generally make forwarding decisionsbased at least upon the layer three network addresses of packets. Oftenrouters modify the frames transversing the router by changing the sourceand/or destination data link, MAC, or hardware addresses when a packetis forwarded. Finally, the more modern usage of the term gateway refersto networking devices that generally make forwarding decisions basedupon information above layer three, the network layer. (Some olderInternet usage of the term gateway basically referred to devicesperforming a layer three routing function as gateways. This usage of theterm gateway is now less common.)

One skilled in the art will be aware of these basic categories ofnetworking devices. Furthermore, often actual networking devicesincorporate functions that are hybrids of these basic categories.Generally, because the preferred embodiments of the present inventioncomprise a physical layer, the preferred embodiments of the presentinvention may be utilized in repeaters, bridges, switches, routers,gateways, hybrid devices and/or any other type of networking device thatutilizes a physical layer interface. “Routing and Switching: Time ofConvergence”, which was published in 2002, by Rita Puzmanova and“Interconnections, Second Edition: Bridges, Router, Switches, andInternetworking Protocols”, which was published in 2000, by RadiaPerlman are two books describing some of the types of networking devicesthat might potentially utilize the preferred embodiments of the presentinvention. These two books are incorporated in their entirety byreference herein.

Overview

In general, the preferred embodiments of the present invention(s)involve many concepts. Because of the large number of concepts of thepreferred embodiments of the present invention, to facilitate easyreading and comprehension of these concepts, the document is dividedinto sections with appropriate headings. None of these headings areintended to imply any limitations on the scope of the presentinvention(s). In general, the “Network Model” section at least partiallycovers the forwarding constructs of the preferred embodiments of thepresent invention(s). The section entitled “Integration Into ExistingCable Network Architectures” generally relates to utilization of thepreferred embodiments of the present invention in cable networkarchitectures. The “Protocol Models” section describes a non-limitingabstract model that might be used to facilitate understanding of thepreferred embodiments of the present invention(s). The “Frame ManagementSublayer (FMS) Data Flows” section describes the formation of FMS dataflows. The section entitled “MPEG Packets” describes the format of MPEGpackets as utilized in the preferred embodiments of the presentinvention(s). The “Network Clocking” section generally coversdistribution of network clock.

The “Downstream Multiplexing” section generally covers the downstreammultiplexing using MPEG packets in the preferred embodiments of thepresent invention(s). The “Upstream Multiplexing” section generallyrelates to upstream multiplexing across one or more active tones. Thesection entitled “Division of Upstream Data” generally relates to thedivision of data into blocks for forward error correction (FEC)processing and to the formation of superframes lasting 2048 symbol clockperiods. The next section is entitled “Upstream Client Transport Modem(cTM) Inverse Multiplexing Sublayer (IMS)” and generally covers upstreammultiplexing in a client transport modem. The section entitled “UpstreamTransport Modem Termination System (TMTS) Inverse Multiplexing Sublayer(IMS)” and generally covers upstream multiplexing in a transport modemtermination system.

In addition, the section entitled “Downstream Client Transport Modem(cTM) Demodulation and Physical Coding Sublayer (PCS)” generally relatesto cTM downstream demodulation. The section entitled “Upstream ClientTransport Modem (cTM) Modulation and Physical Coding Sublayer (PCS)”generally covers cTM upstream modulation. The next section is entitled“Upstream Transport Modem Termination System (TMTS) Demodulation andPhysical Coding Sublayer (PCS)” and generally covers TMTS upstreamdemodulation. Also, the section entitled “Upstream Forward ErrorCorrection (FEC) and Non-Limiting Example with Four Active Tones at 256QAM, 64 QAM, 16 QAM, and QPSK Respectively” generally relates to forwarderror correction. Finally, the section entitled “Client Transport Modem(cTM) and Transport Modem Termination System (TMTS) Physical MediumDependent (PMD) Sublayer” generally relates to physical medium dependentsublayer interfaces.

Network Model

FIG. 1 generally shows one preferred embodiment of the presentinvention. In general, the preferred embodiment of the present inventionallows physical layer connectivity over a cable transmission network105. One skilled in the art will be aware of the types of technologiesand devices used in a cable transmission (CT) network 105. Furthermore,many of the devices and technologies are described in “Modern CableTelevision Technology: Video, Voice, and Data Communications”, which waspublished in 1999, by Walter Ciciora, James Farmer, and David Large. CTnetwork 105 generally has evolved from the networks designed to allowservice providers to deliver community antenna television (CATV, alsoknown as cable TV) to customers or subscribers. However, the networkingtechnologies in CATV may be used by other environments.

Often the terms service provider and subscriber or customer are used toreference various parts of CATV networks and to provide reference pointsin describing the interfaces found in CATV networks. Usually, the CATVnetwork may be divided into service provider and subscriber or customerportions based on the demarcation of physical ownership of the equipmentand/or transmission facilities. Though some of the industry terms usedherein may refer to service provider and/or subscriber reference pointsand/or interfaces, one of ordinary skill in the art will be aware thatthe preferred embodiments of the present invention still apply tonetworks regardless of the legal ownership of specific devices and/ortransmission facilities in the network. Thus, although cabletransmission (CT) network 105 may be a CATV network that is primarilyowned by cable service providers or multiple system operators (MSOs)with an interface at the customer or subscriber premises, one skilled inthe art will be aware that the preferred embodiments of the presentinvention will work even if ownership of all or portions of cabletransmission (CT) network 105 is different than the ownership commonlyfound in the industry. Thus, cable transmission (CT) network 105 may beprivately owned.

As one skilled in the art will be aware, cable transmission (CT) network105 generally is designed for connecting service providers withsubscribers or customers. However, the terms service provider andsubscriber or customer generally are just used to describe the relativerelationship of various interfaces and functions associated with CTnetwork 105. Often the service-provider-side of CT network 105 islocated at a central site, and there are a plurality of subscriber-sideinterfaces located at various remote sites. The terms central and remotealso are just used to refer to the relative relationship of theinterfaces to cable transmission (CT) network 105. Normally, a headendand/or distribution hub is a central location where service providerequipment is concentrated to support a plurality of remote locations atsubscriber or customer premises.

Given this relative relationship among equipment connected to cabletransmission (CT) network 105, the preferred embodiment of the presentinvention may comprise a central cable transmission (CT) physical (PHY)layer transceiver 115. The central CT PHY transceiver (TX/RX) 115generally may have at least one port on the central-side orservice-provider-side of the transceiver 115. Ports 125, 126, 127, 128,and 129 are examples of the central-side ports of central CT PHYtransceiver 115. In general, interface 135 may define the behavior ofcentral CT PHY transceiver 115 with respect to at least one central-sideport such as central-side ports 125, 126, 127, 128, and 129. Interface135 for the central-side ports 125, 126, 127, 128, and 129 may representseparate hardware interfaces for each port of central CT PHY transceiver115. However, interface 135 may be implemented using varioustechnologies to share physical interfaces such that central-side ports125, 126, 127, 128, and 129 may be only logical channels on a sharedphysical interface or media. These logical channels may use variousmultiplexing and/or media sharing techniques and algorithms.Furthermore, one skilled in the art will be aware that the central-sideports 125, 126, 127, 128, and 129 of central CT PHY transceiver 115 maybe serial and/or parallel interfaces and/or buses.

Therefore, the preferred embodiments of the present invention are notlimited to specific implementations of interface 135, and one skilled inthe art will be aware of many possibilities. As a non-limiting example,although central CT PHY transceiver 115 generally is for use inside ofnetworking devices, a serial-interface shared medium such asethernet/802.3 could be used on each of the central-side ports 125, 126,127, 128, and 129 inside of a networking device. Often the decision touse different technologies for interface 135 will vary based on costsand transmission line lengths.

Central CT PHY transceiver 115 further is connected through interface150 to cable transmission (CT) network 105. In addition to thecentral-side or service-provider-side at interface 150 of cabletransmission (CT) network 105, interface 160 generally is on thesubscriber-side, customer-side, or remote-side of cable transmission(CT) network 105. Generally, at least one remote transceiver (such asremote cable transmission (CT) physical (PHY) transceivers 165, 166,167, and 168) is connected to interface 160 on the subscriber-side orremote-side of CT network 105. Each remote CT PHY transceiver 165, 166,and 167 is associated with at least one remote-side port, 175, 176, and177 respectively. Furthermore, remote CT PHY transceiver 168 also isassociated with at least one remote-side port, with the two remote-sideports 178 and 179 actually being shown in FIG. 1. Each remote CT PHYtransceiver 165, 166, 167, and 168 can be considered to have aninterface 185, 186, 187, and 188, respectively, through which itreceives information for upstream transmission and through which itdelivers information from downstream reception.

In general, digital transceivers (such as central CT PHY transceiver 115and remote CT PHY transceivers 165, 166, 167, and 168) comprise atransmitter and a receiver as are generally needed to supportbi-directional applications. Although the preferred embodiments of thepresent invention generally are designed for bi-directionalcommunication, the preferred embodiments of the present inventioncertainly could be used for uni-directional communications without onehalf of the transmitter/receiver pair in some of the transceivers. Ingeneral, digital transmitters basically are concerned with takingdiscrete units of information (or digital information) and forming theproper electromagnetic signals for transmission over networks such ascable transmission (CT) network 105. Digital receivers generally areconcerned with recovering the digital information from the incomingelectromagnetic signals. Thus, central CT PHY transceiver 115 and remoteCT PHY transceivers 165, 166, 167, and 168 generally are concerned withcommunicating information between interface 135 and interfaces 185, 186,187, and 188, respectively. Based on the theories of Claude Shannon, theminimum quanta of information is the base-two binary digit or bit.Therefore, the information communicated by digital transceivers often isrepresented as bits, though the preferred embodiments of the presentinvention are not necessarily limited to implementations designed tocommunicate information in base two bits.

The preferred embodiments of the present invention generally have apoint-to-point configuration such that there generally is a one-to-onerelationship between the central-side ports 125, 126, 127, 128, and 129of the central CT PHY transceiver 115 and the remote-side ports 175,176, 177, 178, and 179, respectively. Like interface 135 for a pluralityof central-side ports 125, 126, 127, 128, and 129, interface 188 with aplurality of remote-side ports 178 and 179 may represent separatehardware interfaces for each port of remote CT PHY transceiver 168.However, interface 188 may be implemented using various technologies toshare physical interfaces such that remote-side ports 178 and 179 mayonly be logical channels on a shared physical interface or media. Theselogical channels may use various multiplexing and/or media sharingtechniques and algorithms. Furthermore, one skilled in the art will beaware that the remote-side ports 178 and 179 of remote CT PHYtransceiver 168 may be serial and/or parallel interfaces and/or buses.

In general, the preferred embodiments of the present invention comprisea one-to-one or point-to-point relationship between active central-sideports and active remote-side ports such that central-side port 125 maybe associated with remote-side port 175, central-side port 126 may beassociated with remote-side port 176, central-side port 127 may beassociated with remote-side port 177, central-side port 128 may beassociated with remote-side port 178, and central-side port 129 may beassociated with remote-side port 179. Though this relationship betweenactive central-side ports and active remote-side ports is one-to-one orpoint-to-point, many technologies such as, but not limited to,multiplexing and/or switching may be used to carry the point-to-pointcommunications between active central-side ports and active remote-sideports.

In general, active ports are allocated at least some bandwidth throughcable transmission (CT) network 105. Normally, most dial-up modem phonecalls through the public switched telephone network (PSTN) areconsidered to be point-to-point connections even though the phone callmay go through various switches and/or multiplexers that often usetime-division multiplexing (TDM). Establishment of an active phone callgenerally allocates bandwidth in the PSTN to carry the point-to-pointcommunications through the PSTN. In a similar fashion, the preferredembodiments of the present invention generally provide point-to-pointconnectivity between active ports of the central CT PHY transceiver 115and the active ports of remote CT PHY transceivers 165, 166, 167, and168. However, the preferred embodiments of the present inventiongenerally work over cable transmission (CT) network 105, which is notlike the generally time-division multiplexed PSTN. (Note: references inthis specification to point-to-point should not be limited to thePoint-to-Point Protocol, PPP, which generally is only one specificprotocol that may be used over point-to-point connections.)

Also, the use of five central-side ports 125, 126, 127, 128, and 129 isnot intended to be limiting and is only shown for example purposes. Ingeneral, central CT PHY transceiver 115 may support at least onecentral-side port. In addition, the use of four remote CT PHYtransceivers 165, 166, 167, and 168 is only for example purposes and isnot intended to be limiting. In general, central CT PHY transceiver 115might communicate with at least one remote CT PHY transceiver (such as165, 166, 167, and 168). Also, each remote CT PHY transceiver 165, 166,167, and 168 may have at least one remote side port, and remote CT PHYtransceiver 168 is shown with a plurality of remote-side ports 178 and179.

FIGS. 2 a and 2 b show further detail on the use of central CT PHYtransceiver 115 and remote CT PHY transceivers 165, 166, 167, and 168 innetworking devices. As shown in FIG. 2 a, central CT PHY transceiver 115generally might be incorporated into a transport modem terminationsystem (TMTS) 215. In addition to central CT PHY transceiver 115, TMTS215 comprises cable transmission (CT) physical layer (PHY) control 217and system control 219. In general, CT PHY control 217 is concerned withhandling bandwidth allocations in cable transmission (CT) network 105,and system control 219 generally is concerned with TMTS managementand/or configuration. Each one of the central-side ports 125, 126, 127,128, and 129 of central CT PHY transceiver 115 may be connected overinterface 135 to central-side network physical layer (PHY) transceivers(TX/RX) 225, 226, 227, 228, and 229, respectively. As discussed withrespect to FIG. 1, interface 135 may actually be some sort of sharedinterface among the various central-side ports (125, 126, 127, 128, and129) and central-side network physical (PHY) transceivers (225, 226,227, 228, and 229).

Generally, most communication systems have transmitters and/or receivers(or transceivers) that handle transmitting and/or receiving signals oncommunication media. Often these transmitters and/or receivers (ortransceivers) are responsible for converting between the electromagneticsignals used to convey information within a device (such as in basebandtransistor-transistor logic (TTL) or complementary metal-oxidesemiconductor (CMOS) signal levels) to electromagnetic signal levelsthat are suitable for transmission through external media that may bewired, wireless, waveguides, electrical, optical, etc. Althoughinterface 135 is shown as individual connections between thecentral-side ports 125, 126, 127, 128, and 129 of central CT PHYtransceiver 115 and central-side network PHY transceivers 225, 226, 227,228, and 229, one skilled in the art will be aware that many possibleimplementations for interface 135 are possible including, but notlimited, to serial interfaces, parallel interfaces, and/or buses thatmay use various technologies for multiplexing and or access control toshare at least one physical communications medium at interface 135.

In general, central-side network physical interfaces 225, 226, 227, 228,and 229 are connected to central networks 235, 236, 237, 238, and 239,respectively. Based upon the policy decisions of the service provider(and/or the owners of the TMTS 215 and of the associated central-sidenetwork PHY transceivers 225, 226, 227, 228, and/or 229), centralnetworks 235, 236, 237, 238, and 239 may be connected together into acommon network 240. One skilled in the art will be aware that manydifferent configurations for connecting central networks 235, 236, 237,238, and 239 are possible based upon different policy decisions of theowners of the equipment and any customers paying for connectivitythrough the equipment.

Central-side network PHY transceivers 225, 226, 227, 228, and 229generally are connected over interface 245 to central networks 235, 236,237, 238, and 239, respectively. In the preferred embodiment of thepresent invention central-side network PHY transceivers 225, 226, 227,228, and 229 are ethernet/802.3 interfaces, and each ethernet/802.3interface may be connected to a separate central network. However, otherconnections for interface 245 are possible that allow one or moretransmission media to be shared using various techniques and/or mediaaccess control algorithms the may perform various multiplexingstrategies. Although one skilled in the art will be aware that variousmethods could be used to share communications media at interface 245, ingeneral having separate ethernet/802.3 ports and/or separate T1 ports(i.e., N×56/64 ports) at interface 135 for each central-side network PHYtransceiver 225, 226, 227, 228, and 229 offers maximum flexibility inallowing service providers or equipment owners to make policy decisionsand also offers low cost based on the ubiquitous availability ofethernet/802.3 interfaces and equipment.

Furthermore, one skilled in the art will be aware that there are manydata speeds and physical layer specifications for ethernet/802.3. Ingeneral, the preferred embodiments of the present invention will workwith any of the ethernet/802.3 specifications. Thus, if central-sidenetwork physical (PHY) transceivers (TX/RX) 225, 226, 227, 228, and 228are ethernet/802.3 interfaces, they may utilize any of theethernet/802.3 speeds and/or physical layer interfaces. Also, eachcentral-side PHY transceiver 225, 226, 227, 228, and 229 might use adifferent ethernet/802.3 speed and/or a physical layer specificationfrom any of the other central-side network PHY transceivers 225, 226,227, 228, and 229.

FIG. 2 b generally shows the remote-side, customer-side, orsubscriber-side equipment and connections, whereas FIG. 2 a generallyshows the central-side or service-provider-side equipment andconnections. In FIG. 2 b, cable transmission (CT) network 105 isrepeated from FIG. 2 a. In addition, FIG. 2 a shows the four remote CTPHY transceivers 165, 166, 167, 168, and 169 as they might be usedinside client transport modems (cTMs) 265, 266, 267, and 268,respectively.

Client transport modem 265 comprises remote CT PHY transceiver 165 thatis connected through connection 175 across interface 185 to at least oneremote-side network physical layer (PHY) transceiver (TX/RX) 275. Also,client transport modem 266 comprises remote CT PHY transceiver 166 thatis connected through connection 176 across interface 186 to at least oneremote-side network physical layer (PHY) transceiver (TX/RX) 276. Inaddition, client transport modem 267 comprises remote CT PHY transceiver167 that is connected through connection 177 across interface 187 to atleast one remote-side network physical layer (PHY) transceiver (TX/RX)277. Finally, client transport modem 268 comprises remote CT PHYtransceiver 168 that is connected through connection 178 acrossinterface 188 to at least one remote-side network physical layer (PHY)transceiver (TX/RX) 278 and that is connected through connection 179across interface 189 to at least one remote-side network physical layer(PHY) transceiver (TX/RX) 279.

In general, the use of four client transport modems (cTMs) 265, 266,267, and 268 in FIG. 2 b is only for illustrative purposes and is notmeant to imply any limitations on the number of client transport modems(cTMs) that may be supported. Furthermore, one skilled in the art willbe aware that based upon networking needs the capabilities of multipleclient transport modems (cTMs) could be integrated into a single unit.Thus, a single unit connected to the customer-side, subscriber-side, orremote-side of the cable transmission (CT) network 105 could actuallyhave a plurality of remote CT PHY transceivers.

In general, the remote-side network physical (PHY) transceivers (TX/RX)275, 276, 277, 278, and 279 are connected across interfaces 285, 286,287, 288, and 289 to remote networks 295, 296, 297, 298, and 299,respectively. In the preferred embodiment of the present inventioninterfaces 285, 286, 287, 288, and/or 289 are ethernet/802.3 interfaces.However, one skilled in the art will be aware that other interfaces andtechnologies might be used with the concepts disclosed in thisspecification. As a non-limiting example, an interface of a clienttransport modem (cTM) might be used to support circuit emulationservices (CES) to carry N×56 kbps and/or N×64 kbps (where N is apositive integer) digital data streams. One skilled in the art will beaware that various N×56 and N×64 configurations are commonly designatedas various digital speeds such as, but not limited to, DS0, DS1, DS3,etc. Also, one skilled in the art will be aware that the various N×56and/or N×64 services are often delivered over plesiochronous digitalhierarchy (PDH) interfaces such as, but not limited to, T1, T3, etc.and/or synchronous digital hierarchy (SDH) interfaces such as, but notlimited to, Synchronous Transport Signal, Level 1 (STS-1), STS-3, etc.Often the STS frames are carried in a synchronous optical network(SONET) on optical carriers that are generally referred to as OC-1(optical carrier 1), OC-3, etc. In addition, to these higher ordermultiplexing of multiple DS0s, interfaces such as switched 56/64 andbasic rate interface (BRI) ISDN offer support for smaller numbers of56/64 kbps DS0s.

One skilled in the art will be aware of these various N×56 and N×64technologies and how they generally can be used to connect devices tonetworks such as the PSTN (public switched telephone network). Inaddition, one skilled in the art will be aware that such digital N×56and N×64 kbps connections also may carry digitized voice generally usingpulse code modulation (PCM) and various companding techniques such as,but not limited to, A-law and mu-law. Therefore, the remote-side networkphysical (PHY) transceivers (TX/RX) 275, 276, 277, 278, and 279 do notall have to use 802.3/ethernet. In at least one preferred embodiment ofthe present invention, a client transport modem (cTM) 268 with aplurality of remote-side network physical (PHY) transceivers (TX/RX) 278and 279 may support different types of interfaces for each transceiverat interfaces 288 and 289. Thus, as a non-limiting example, remote-sidenetwork physical (PHY) transceiver 278 may use ethernet/802.3 to connectto an ethernet/802.3 remote network 298, and remote-side networkphysical (PHY) transceiver 279 may be a T1 interface to remote network299. This non-limiting example configuration is expected to be commonfor many remote offices that need ethernet/802.3 connectivity to carrydata and packetized real-time services such as voice or video and thatalso need T1 interfaces to connect to legacy circuit-switched voice fordevices such as PBXs (Private Branch Exchanges).

Furthermore, one skilled in the art will be aware that there are manydata speeds and physical layer specifications for ethernet/802.3. Ingeneral, the preferred embodiments of the present invention will workwith any of the ethernet/802.3 specifications. Thus, if remote-sidenetwork physical (PHY) transceivers (TX/RX) 275, 276, 277, 278, and 279are ethernet/802.3 interfaces, they may utilize any of theethernet/802.3 speeds and/or physical layer interfaces. Also, eachremote-side PHY transceiver 275, 276, 277, 278, and 279 might use adifferent ethernet/802.3 speed and/or physical layer specification fromany of the other remote-side network PHY transceivers 275, 276, 277,278, and 279.

In general, the preferred embodiments of the present invention might beconsidered as providing repeater functionality between the central-sidenetwork PHY transceivers 225, 226, 227, 228, and 229 and remote-sidenetwork PHY transceivers 275, 276, 277, 278, and 279, respectively.Generally, the repeater service may involve corresponding central-sideand remote-side interfaces and transceivers having the same speeds.However, one skilled in the art will be aware that ethernet/802.3 hubsare repeaters and that some ethernet/802.3 hubs handle speed conversionssuch as between 10 Mbps ethernet/802.3 and 100 Mbps fast ethernet/802.3.Thus, one skilled in the art will be aware of using the techniques foundin these multi-speed ethernet/802.3 hubs to support different speeds onthe interfaces of corresponding central-side and remote-side networkphysical (PHY) transceivers (TX/RX) and generally still provide repeaterfunctionality. Also, one skilled in the art will be aware that even if acentral-side network physical transceiver (such as, but limited to,central-side network physical transceiver 225) and a correspondingremote-side network physical transceiver (such as, but limited to,remote-side network physical transceiver 275) operate at the same datarate, the transceivers may use different types of physical media andportions of the ethernet/802.3 specification such as, but not limitedto, 100BaseTX on copper for a central-side network physical transceiverand 100BaseFX on fiber for a remote-side network physical transceiver.

Given the general point-to-point relationship between central-sidenetwork physical (PHY) transceivers (TX/RX) 225, 226, 227, 228, and 229with the corresponding remote-side network physical (PHY) transceivers(TX/RX) 275, 276, 277, 278, and 279, respectively, the client transportmodems (cTMs) 265, 266, 267, and 268 can each be thought of as having acorresponding server transport modem (sTM) 325, 326, 327, and 328,respectively, as shown in FIG. 3. In general, the server transportmodems (sTMs) 325, 326, 327, and 328 may not be separate equipment, butmay instead be implemented using shared hardware in TMTS 215 in thepreferred embodiment of the present invention. Although to each clienttransport modem (cTM) 265, 266, 267, and 268 it may seem like there is aconnection to a dedicated server transport modem (sTM), (such as sTMs325, 326, 327, and 328, respectively), the server transport modems maynot be actual individual hardware in the preferred embodiment of thepresent invention. Even though the preferred embodiments of the presentinvention may not use individual server transport modems, this does notpreclude such implementations.

In the FIG. 3 representation of the preferred embodiments of the presentinvention, the server transport modems (sTMs) 325, 326, 327, and 328 aswell as the corresponding connections to the client transport modems(cTMs) 265, 266, 267, and 268, respectively, are shown as small dashedlines to indicate the virtual nature of the relationship. The servertransport modems (sTMs) 325, 326, 327, and 328 may be virtual in thepreferred embodiments of the present invention because they generallymay be implemented using shared hardware in TMTS 215.

In general, the preferred embodiments of the present invention may actto transparently repeat digital signals between interfaces 245 and 385.Interfaces 245 and/or 385 may have different types of technologiesand/or media for the point-to-point connections between active ports oninterface 245 and active ports on interface 385. Active ports generallyare associated with point-to-point connections between TMTS 215 and aclient transport modem 265, 266, 267, or 268, when the point-to-pointconnection is allocated bandwidth through cable transmission (CT)network 105. In general, TMTS 215 connects at interface 250 to thecentral-side or service-provider-side of cable transmission (CT) network105, whereas client transport modems (cTMs) 265, 266, 267, and 268connect at interface 260 to the remote-side, customer-side, orsubscriber-side of cable transmission (CT) network 105. Furthermore, theclient transport modems (cTMs) 265, 266, 267, and 268 may be connectedto remote networks over interface 385 using various types of media andtechnologies. The transport modem termination system (TMTS) 215connected at interface 245 may further be connected into a commonnetwork 240, although the technology of the preferred embodiments of thepresent invention allows other central network configurations based uponvarious policy decisions and network ownership requirements. Some ofthese considerations include, but are not limited to, privacy, security,cost, and/or connectivity.

Integration Into Existing Cable Network Architectures

FIG. 4 shows a more detailed implementation of the preferred embodimentof the present invention from FIGS. 1 through 3 and its use in a cablenetwork that may carry additional services over the cable transmission(CT) network 105. FIG. 4 shows TMTS 215 and cTMs 265, 266, 267, and 268that were briefly described with respect to FIGS. 2 a and 2 b. As shownin FIG. 4, each cTM 265, 266, 267, and 268 has at least oneethernet/802.3 physical (PHY) transceiver 475, 476, 477, and 478,respectively. The ethernet/802.3 PHY transceivers 475, 476, 477, and 478correspond to one non-limiting type of transceiver that may be used inthe preferred embodiment of the present invention for remote-sidenetwork physical (PHY) transceivers (TX/RX) 275, 276, 277, 278, and 279at the associated interfaces 285, 286, 287, 288, and 289 of FIG. 2 b.Also each cTM 265, 266, 267, 268 may have one or a plurality of physicaltransceivers at interface 385. Each one of these transceivers may be anethernet/802.3 physical interface or any other type of communicationsinterface.

Furthermore, those skilled in the art will be aware of the relativelyminor differences between IEEE 802.3 and the Digital-Intel-Xerox (DIX)2.0 (or II) specification of ethernet and the possibility of carryingmultiple frame formats such as, but not limited to, ethernet_II, 802.3raw, 802.3/802.2 LLC (logical link control), and 802.3/802.2 SNAP(Sub-Network Access Protocol) on networks colloquially known asethernet. In addition, the preferred embodiments of the presentinvention also are intended to cover other versions and variations ofethernet/802.3 including, but not limited to, DIX ethernet 1.0.References in this specification to ethernet and/or IEEE 802.3 generallyare intended to refer to networks capable of carrying any combination ofthe various frame types generally carried on such ethernet/802.3networks. Because the preferred embodiments of the present inventiongenerally provide a physical layer interface that may be used forrepeater service, the preferred embodiments of the present inventiongenerally are transparent to the various types of ethernet/802.3 frames.

Although FIG. 4 shows four cTMs and four interfaces on TMTS 215, this isonly for illustrative purposes, and the preferred embodiments of thepresent invention are not limited to providing connectivity to exactlyfour client transport modems. Instead the preferred embodiment of thepresent invention will work with at least one client transport modem andat least one corresponding interface on TMTS 215. In general, in FIG. 4each one of the 802.3 physical (PHY) layer interfaces or transceivers475, 476, 477, and 478 of the client transport modems (cTMs) generallyis associated with a corresponding 802.3 physical layer interface and/ortransceiver 425, 426, 427, and 428, respectively, in the TMTS 215. Ingeneral, 802.3 physical layer interfaces and/or transceivers 425, 426,427, and 428 are one non-limiting example of the types of transceiversthat may be used in the preferred embodiment of the present inventionfor central-side network physical (PHY) transceivers (TX/RX) 225, 226,227, 228, and 229 at the associated interface 245 of FIG. 2 a.

As shown in FIG. 4, the 802.3 PHY interfaces and/or transceivers 425,426, 427, and 428 of the TMTS 215 are further connected to a headendnetworking device such as hub, switch, and/or router 430 with 802.3 PHYinterfaces and/or transceivers 435, 436, 437, and 438, respectively.Those skilled in the art will be aware that this is only one of the manypossible ways of connecting the ethernet/802.3 PHY interfaces and/ortransceivers 425, 426, 427, and 428 of TMTS 215 to a service-providercommon network 240 that may include a service provider backbone network(not shown in FIG. 4). Generally, based on service provider policies andequipment costs, various choices may be made for the specific device(s)to be connected to the 802.3 PHY interfaces and/or transceivers 225,226, 227, and 228 of TMTS 215. As a non-limiting example, two of the802.3 PHY interfaces and/or transceivers 225, 226, 227, and 228 may beassociated with providing connectivity to two different remote officesof a particular company. That company may just want those two 802.3 PHYinterfaces and/or transceivers of TMTS 215 to be directly connected(possibly using an ethernet cross-over cable that is known to one ofskill in the art by crossing pins 1 and 3 as well as pins 2 and 6 of anRJ45 connector).

Therefore, the 802.3 PHY interfaces and/or transceivers 425, 426, 427,and 428 of TMTS 215 can be connected based on service provider policiesand/or subscriber (or customer) demands. In addition, the presentinvention is not limited to a specific type of network device or linkused to connect the 802.3 PHY interfaces port 225, 226, 227, and 228 ofTMTS 215 to a service provider's network, which may be a common network240 and may include a backbone network (not shown in FIG. 4). Thus, theat least one connection to headend hub/switch/router 430 over interface245 is only one non-limiting example of how the TMTS 215 can beconnected to a service provider backbone network.

Furthermore, as described with respect to FIGS. 1 through 3, thepreferred embodiment of the present invention basically functions as aethernet/802.3 repeater that transparently copies the bits fromethernet/802.3 frames between interfaces 245 and 385 of FIGS. 3 and 4.The transparent support of ethernet/802.3 generally allows the system totransparently carry ethernet/802.3 frames with virtual LAN orlabel-based multiplexing information such as, but not limited to, theinformation defined in IEEE 802.1Q (VLAN or Virtual LAN) and/or IEEE802.17 (RPR or Resilient Packet Ring). Because of the transparency ofthe preferred embodiment of the present invention to various ethernetvirtual LAN and/or tag/label information, service providers using thepreferred embodiment of the present invention generally have theflexibility to specify policies for carrying, combining, and/orsegregating the traffic of different subscribers based on the types ofdevices connected to interfaces 245 and 385. Also, subscribers orcustomers may choose to implement various mechanisms such as, but notlimited to, 802.1Q VLAN and/or 802.17 RPR that might be used between twoor more subscriber sites that are each connected to the preferredembodiment of the present invention. The transparency of the preferredembodiment of the present invention to this additional information inethernet/802.3 frames provides versatility to the service provider andthe subscriber in deciding on how to use various VLAN, tag, and/or labelmechanisms that are capable of being carried with ethernet/802.3 frames.

In addition, FIG. 4 further shows how one client transport modem (cTM)265 with at least one 802.3 PHY interface or transceiver 475 isconnected over interface 385 to 802.3 PHY interface or transceiver 485.Ethernet/802.3 PHY interface 485 may be located in a subscriberhub/switch/router 480 that has more 802.3 PHY interfaces or transceivers491, 492, and 493 into the customer or subscriber LANs or networks,which are non-limiting examples of portions of remote networks. Theother client transport modems (cTMs) 266, 267, and 268 also would likelyhave connections over interface 385 to various devices of other customeror subscriber LANs, though these are not shown in FIG. 4. Much likeheadend hub/switch/router 430, the actual type of network device orconnection for subscriber hub/switch/router 480 is not limited by thepreferred embodiment of the present invention. The preferred embodimentof the present invention generally provides transparent ethernetrepeater capability over a cable transmission network 105. In FIG. 4,the interfaces 250 and 260 generally correspond to the central-side orservice-provider-side and to the remote-side, customer-side, orsubscriber-side, respectively, of cable transmission (CT) network 105.These reference interfaces 250 and 260 in FIG. 4 were shown in FIGS. 2a, 2 b, and 3 as the interfaces of cable transmission (CT) network 105.

Those skilled in the art will be aware of the devices and technologiesthat generally make up cable transmission networks 105. At least some ofthis cable transmission technology is described in “Modern CableTelevision Technology: Video, Voice, and Data Communications” by WalterCiciora, James Farmer, and David Large, which is incorporated byreference in its entirety herein. In general, the cable transmissionnetworks 105 may carry other services in addition to those of thepreferred embodiment of the present invention. For instance, as known byone skilled in the art, a cable transmission network 105 may carryanalog video, digital video, DOCSIS data, and/or cable telephony inaddition to the information associated with the preferred embodiment ofthe present invention. Each one of these services generally hasequipment located at the service provider, such as analog videoequipment 401, digital video equipment 402, DOCSIS data equipment 403,and cable telephony equipment 404 as well as equipment located atvarious customer or subscriber locations such as analog video equipment411, digital video equipment 412, DOCSIS data equipment 413, and cabletelephony equipment 414. Even though these other services in FIG. 4 areshown as if they are bi-directional, often some of the services such asanalog video and digital video have historically been primarilyuni-directional services that generally are broadcast from the headendto the subscribers.

In addition, FIG. 4 further shows some of the transmission equipmentthat might be used in a cable transmission network 105 (generally foundbetween interfaces 250 and 260 in FIG. 4). For example, cabletransmission networks 105 might include combiner 415 and splitter 416 tocombine and split electromagnetic signals, respectively. As cabletransmission network 105 may be a hybrid fiber-coax (HFC) network, itcould contain devices for converting electromagnetic signals betweenelectrical and optical formats. For example, downstreamoptical/electrical (O/E) interface device 417 may convert downstreamelectrical signals (primarily carried over coaxial cable) to downstreamoptical signals (primarily carried over fiber optic lines). Also,upstream optical/electrical (O/E) interface device 418 may convertupstream optical signals (primarily carried over fiber optic lines) toupstream electrical signals (primarily carried over coaxial cable).Downstream optical/electrical interface 417 and upstreamoptical/electrical interface 418 generally are connected to a subscriberor customer premises over at least one fiber optic connection tooptical/electrical (O/E) interface 420. The downstream opticalcommunications between downstream O/E interface 417 and O/E interface420 might be carried on different optical fibers from the fiberscarrying upstream optical communications between O/E interface 420 andupstream O/E interface 418. However, one skilled in the art will beaware that a variation on frequency-division multiplexing (FDM) known aswavelength division multiplexing (WDM) could be used to allowbi-directional duplex transmission of both the downstream and upstreamoptical communications on a single fiber optic link.

Generally, for an HFC system the interfaces at customer or subscriberpremises are electrical coax connections. Thus, optical/electricalinterface 420 may connect into a splitter/combiner 422 that dividesand/or combines electrical signals associated with analog video device411, digital video device 412, DOCSIS data device 413, and/or cabletelephone device 413 that generally are located at the customer orsubscriber premises. This description of the splitters, combiners, andoptical electrical interfaces of HFC networks that may be used for cabletransmission network 105 is basic and does not cover all the other typesof equipment that may be used in a cable transmission network 105. Somenon-limiting examples of other types of equipment used in a cabletransmission network 105 include, but are not limited to, amplifiers andfilters. Those skilled in the art will be aware of these as well as manyother types of devices and equipment used in cable transmissionnetworks.

Furthermore, one skilled in the art will be aware that the preferredembodiments of the present invention may be used on all-coax, all-fiber,and/or hybrid fiber-coax (HFC) such as cable transmission networks (CT)105. In general, cable transmission (CT) network 105 generally is aradio frequency (RF) network that generally includes somefrequency-division multiplexed (FDM) channels. Also, one skilled in theart will be aware that the preferred embodiments of the presentinvention may be used on a cable transmission (CT) network 105 thatgenerally is not carrying information for other applications such as,but not limited to, analog video, digital video, DOCSIS data, and/orcable telephony. Alternatively, the preferred embodiments of the presentinvention may coexist on a cable transmission (CT) network 105 that iscarrying information analog video, digital video, DOCSIS data, and/orcable telephony as well as various combinations and permutationsthereof. Generally in the preferred embodiments of the presentinvention, the cable transmission (CT) network 105 is any type ofnetwork capable of providing frequency-division multiplexed (FDM)transport of communication signals such as but not limited to electricaland/or optical signals. The FDM transport includes the variation of FDMin optical networks which is generally called wavelength-divisionmultiplexing (WDM).

In addition, the preferred embodiments of the present invention may useone or more MPEG PIDs for downstream transmission of MPEG packetscarrying the traffic of Frame Management Sublayer (FMS) data flows. Inaddition, MPEG packets carrying the octets of one or more FMS data flowsof the preferred embodiments of the present invention are capable ofbeing multiplexed into the same frequency channel of a cabletransmission network that also carries other MPEG packets that havedifferent PID values and that generally are unrelated to the FMS dataflows of the preferred embodiments of the present invention. Thus, notonly are both the upstream and the downstream frequency channel usagesof the preferred embodiments of the present invention easily integratedinto the general frequency-division multiplexing (FDM) bandwidthallocation scheme commonly-found in cable transmission networks, butalso the use of the MPEG frame format for downstream transmission in thepreferred embodiments of the present invention allows easy integrationinto the PID-based time-division multiplexing (TDM) of MPEG 2 transportstreams that also is commonly-found in cable transmission networks.Thus, one skilled in the art will be aware that the preferredembodiments of the present invention can be easily integrated into thefrequency-division multiplexing (FDM) architecture of cable transmissionnetworks.

As one skilled in the art will be aware, in North America cabletransmission networks generally were first developed for carrying analogchannels of NTSC (National Television Systems Committee) video thatgenerally utilize 6 MHz of frequency bandwidth. Also, one skilled in theart will be aware that other parts of the world outside North Americahave developed other video coding standards with other cabletransmission networks. In particular, Europe commonly utilizes the phasealternating line (PAL) analog video encoding that is generally carriedon cable transmission networks in frequency channels with a little morebandwidth than the generally 6 MHz channels, which are commonly used inNorth American cable transmission networks. Because the frequencychannels used in the preferred embodiments of the present invention willfit into the more narrow frequency bandwidth channels that wereoriginally designed to carry analog NTSC video, the frequency channelsused in the preferred embodiments of the present invention also will fitinto larger frequency bandwidth channels designed for carrying analogPAL video.

In addition, although the preferred embodiments of the present inventionare designed to fit within the 6 MHz channels commonly-used for analogNTSC signals and will also fit into cable transmission networks capableof carrying analog PAL signals, one skilled in the art will be awarethat the multiplexing techniques utilized in the preferred embodimentsof the present invention are general. Thus, the scope of the embodimentsof the present invention is not to be limited to just cable transmissionsystems, which are designed for carrying NTSC and/or PAL signals.Instead, one skilled in the art will be aware that the concepts of theembodiments of the present invention generally apply to transmissionfacilities that use frequency division multiplexing (FDM) and have aone-to-many communication paradigm for one direction of communication aswell as a many-to-one communication paradigm for the other direction ofcommunication.

Furthermore, the preferred embodiments of the present inventiongenerally communicate using signals with similar transmissioncharacteristics to other signals commonly found in cable transmissionnetworks. Thus, one skilled in the art will be aware that the signaltransmission characteristics of the preferred embodiments of the presentinvention are designed to integrate into existing, already-deployedcable transmission networks that may be carrying other types of signalsfor other services such as, but not limited to, analog and/or digitalvideo, analog and/or digital audio, and/or digital data. The preferredembodiments of the present invention are designed to be carried in thesame communications medium that also may be carrying the other serviceswithout the preferred embodiments of the present invention introducingundesirable and unexpected interference on the other services.Furthermore, the preferred embodiments of the present invention willoperate over various types of communication media including, but notlimited to, coaxial (coax) cable, fiber, hybrid fiber-coax, as well aswireless. Because the preferred embodiments of the present inventiongenerally are designed to conform to some of the historical legacystandards of cable networks, the preferred embodiments of the presentinvention can be used in many existing network infrastructures that arealready carrying other services. Therefore, the preferred embodiments ofthe present invention peacefully coexist with existing historical legacyservices. Also, the preferred embodiments of the present invention canbe used in other environments that are not limited by historical legacyservices (or services compatible with historical legacy standards).

FIGS. 5 a and 5 b generally show a more detailed system referencediagram for a communication system that might be using a preferredembodiment of the present invention. In general, FIG. 5 a covers atleast some of the equipment and connections commonly found on thecentral-side or service-provider-side in a system using the preferredembodiments of the present invention. In contrast, FIG. 5 b generallycovers at least some of the equipment and connections commonly found onthe remote-side, customer-side, or subscriber-side of a system using thepreferred embodiments of the present invention. Generally, theapproximate demarcation of cable transmission network (CT) 105 networkis shown across the FIGS. 5 a and 5 b. One skilled in the art will beaware that the devices shown in FIGS. 5 a and 5 b are non-limitingexamples of the types of equipment generally found in RF cable networks.Thus, FIGS. 5 a and 5 b show only a preferred embodiment of the presentinvention and other embodiments are possible.

In general, the equipment for the central-side, service-provider side,and/or customer-side of the network generally may be located in adistribution hub and/or headend 510. FIG. 5 a shows transport modemtermination system (TMTS) 215 comprising at least one cable transmission(CT) physical (PHY) transceiver (TX/RX) 115, at least one cabletransmission (CT) physical (PHY) control (CTRL) 217, at least systemcontrol (SYS CTRL) 219, and at least one central-side network physical(PHY) transceiver (TX/RX) 225. In the preferred embodiments of thepresent invention, TMTS 215 supports two types of interfaces to commonnetwork 240. In FIG. 5 a these two types of interfaces are shown as TMTS802.3 interface 531 and TMTS circuit emulation service (CES) interface532. In general, there may be multiple instances of both TMTS 802.3interface 531 and TMTS CES interface 532 that might be used to handletraffic for multiple remote-side network interfaces and/or transceiverson a single client transport modem (cTM) or for multiple remote-sidenetwork interfaces on a plurality of client transport modems (cTMs).

In the preferred embodiment of the present invention the at least oneTMTS 802.3 interface 531 generally is capable of transparently conveyingthe information in ethernet/802.3 frames. Generally, at the most basiclevel, the preferred embodiments of the present invention are capable ofacting as an ethernet/802.3 physical layer repeater. However, oneskilled in the art will be aware that the generally physical layerconcepts of the preferred embodiments of the present invention may beintegrated into more complex communication devices and/or systems suchas, but not limited to, bridges, switches, routers, and/or gateways.

Generally, at least one TMTS CES interface 532 provides circuitemulation capability that may be used to carry generally historical,legacy interfaces that are commonly associated with circuit-switchednetworks, such as the public switched telephone network (PSTN). Thoseskilled in the art will be aware of analog and/or digital interfaces tothe PSTN that are commonly found in devices interfacing to the PSTN. Indigital form, these interfaces often comprise integer multiples of a DS0at 56 kbps (N×56) and/or 64 kbps (N×64). Also, a person skilled in theart will be aware of various common multiplexing technologies that maybe used to aggregate the integer multiples of DS0s. These multiplexingtechnologies generally can be divided into the plesiochronous digitalhierarchy (PDH) and the synchronous digital hierarchy (SDH) that arewell-known to one of ordinary skill in the art.

In general, at least one TMTS 802.3 interface 531 may be connected intoa headend hub, switch, or router 535 or any other networking device toimplement various policy decisions for providing connectivity betweenthe transport modem termination system 215 and the client transportmodems (cTMs) 265. One skilled in the art generally will be aware of thevarious policy considerations in choosing different types of networkingdevices and/or connections for connecting to TMTS 802.3 interface 531.

Furthermore, at least one TMTS CES interface 532 might be connected to atelco concentrator that generally might be various switching and/ormultiplexing equipment designed to interface to technologies generallyused for carrying circuit-switched connections in the PSTN. Thus, telcoconcentrator 536 might connect to TMTS 215 using analog interfacesand/or digital interfaces that generally are integer multiples of DS0(56 kbps or 64 kbps). Some non-limiting examples of analog interfacesthat are commonly found in the industry are FXS/FXO (foreign exchangestation/foreign exchange office) and E&M (ear & mouth). In addition tocarrying the actual information related to CES emulation service betweenTMTS 215 and telco concentrator 536, TMTS CES interface 532 also may tocarry various signaling information for establishing and releasingcircuit-switched calls. One skilled in the art will be aware of manydifferent signaling protocols to handle this function, including but notlimited to, channel associated signaling using bit robbing, Q.931D-channel signaling of ISDN, standard POTS signaling as well as manyothers.

In general, one or more devices at the headend, such as headend hub,switch, and/or router 535, generally provide connectivity between TMTS215 and backbone network 537, which may provide connectivity to varioustypes of network technology and/or services. Also, telco concentrator536 may be further connected to the public switched telephone network(PSTN). In general, telco concentrator 536 might provide multiplexingand/or switching functionality for the circuit emulation services (CES)before connecting these services to the PSTN. Also, telco concentrator536 could convert the circuit emulation services (CES) into packet-basedservices. For example, 64 kbps PCM voice (and associated signaling)carried across TMTS CES interface 532 might be converted into variousforms of packetized voice (and associated signaling) that is carried ona connection between telco concentrator 536 and headend hub, switch,and/or router 535. In addition, the connection between telcoconcentrator 536 and headend hub, switch, and/or router 535 may carrynetwork management, configuration, and/or control information associatedwith telco concentrator 536.

In general, TMTS 802.3 interface 531 and TMTS CES interface 532 may beconsidered to be at least part of the headend physical (PHY) interfacenetwork 540. Also, at least part of the common network 240 generally maybe considered to be the backbone interface network 541. In addition tothe systems and interfaces generally designed for transparently carryinginformation between the central-side networks (as represented at TMTS802.3 interface 531 and TMTS CES interface 532) of the TMTS 215 and theremote-side networks of at least one cTM 265, the communication systemgenerally has connections to local server facilities 543 and operations,administration, and maintenance system 544 that may both be part ofcommon network 240. Network management, configuration, maintenance,control, and administration are capabilities that, although optional,are generally expected in many communication systems today. Though thepreferred embodiments of the present invention might be implementedwithout such functions and/or capabilities, such an implementationgenerally would be less flexible and would probably be significantlymore costly to support without some specialized network functions suchas, but not limited to, operations, administration, and maintenance(OA&M) 544. Also, local server facility 543 may comprise servers runningvarious protocols for functions such as, but not limited to, dynamicnetwork address assignment (potentially using the dynamic hostconfiguration protocol—DHCP) and/or software uploads as well asconfiguration file uploads and downloads (potentially using the trivialfile transfer protocol—TFTP).

FIG. 5 a further shows how cable transmission (CT) physical (PHY)transceiver (TX/RX) 115 in TMTS 215 might interface to RF interfacenetwork 550 in the preferred embodiment of the present invention. In anembodiment of the present invention, CT PHY transceiver 115 connects toa TMTS asynchronous serial interface (ASI) 551 for the downstreamcommunication from TMTS 215 towards at least one client transport modem(cTM) 265. In a preferred embodiment of the present invention, the QAM(Quadrature Amplitude Modulation) modulator 552 is external to the TMTS215. One skilled in the art will be aware that other embodiments of thepresent invention are possible that may incorporate the at least one QAMmodulator 552 into the TMTS 215 for downstream communication.Furthermore, an ASI (asynchronous serial interface) interface is onlyone non-limiting example of a potential interface for the at least oneQAM modulator 522. QAM modulators 552 with ASI interfaces are commonlyused in cable transmission networks 105, and reuse of existingtechnology and/or systems may allow lower cost implementations of thepreferred embodiments of the present invention. However, otherembodiments using various internal and/or external interfaces to variouskinds of modulators might be used in addition to or in place of the TMTSASI interface 551 to at least one QAM modulator 552.

Because QAM modulators are used for many types of transmission in CATVnetworks, one skilled in the art will be aware of many interfaces (bothinternal and external) that might be used for connecting QAMmodulator(s) 522 for downstream transmission. The TMTS ASI interface 551is only one non-limiting example of an interface that is often used inthe art and is well-known to one of ordinary skill in the art. As oneskilled in the art will be aware, such QAM modulators have been used inCATV networks to support downstream transmission for commonly-deployedservices such as, but not limited to, DOCSIS cable modems and digital TVusing MPEG video. Due to the common usage of such QAM modulators fordigital services and the large variety of external and internalinterfaces used by many vendors' equipment, one skilled in the art willbe aware that many types of interfaces may be used for transmitting thedigital bit streams of a TMTS to QAM modulators for modulation followedby further downstream transmission over cable transmission networks.Thus, in addition to TMTS ASI interface 551, one skilled in the art willbe aware of other standard and/or proprietary interfaces that may beinternal or external to TMTS 215 and that might be used to communicatedigital information to QAM modulator(s) 522 for downstream transmission.These other types of interfaces to QAM modulators are intended to bewithin the scope of the embodiments of the present invention.

In general, TMTS 215 controls the downstream modulation formats andconfigurations in the preferred embodiments of the present invention.Thus, when external modulators (such as QAM modulator 552) are used withTMTS 215, some form of control messaging generally exists between TMTS215 and QAM modulator 552. This control messaging is shown in FIG. 5 aas QAM control interface 553, which generally allows communicationbetween at least one QAM modulator 552 and TMTS 215. In the preferredembodiment of the present invention, this communication between at leastone QAM modulator 552 and TMTS 215 may go through headend hub, switch,and/or router 535 as well as over TMTS 802.3 interface 531.

Furthermore, modulators such as, but not limited to, at least one QAMmodulator 552 often are designed to map information onto a set ofphysical phenomena or electromagnetic signals that generally are knownas a signal space. Generally a signal space with M signal points isknown as a M-ary signal space. In general, a signal space with M signalpoints may completely encode the floor of log₂ M bits or binary digitsof information in each clock period or cycle. The floor of log₂ M issometimes written as floor(log₂ M) or as └log₂ M┘. In general, the floorof log₂ M is the largest integer that is not greater than log₂ M. When Mis a power of two (i.e., the signal space has 2, 4, 8, 16, 32, 64, etc.signal points), then the floor of log₂ M generally is equal to log₂ M,and log₂ M generally is known as the modulation index. Because theminimum quanta of information is the base-two binary digit or bit, theinformation to be mapped into a signal space generally is represented asstrings of bits. However, one skilled in the art will be aware that thepreferred embodiment of the present invention may work withrepresentations of information in other number bases instead of or inaddition to base two or binary.

As known to those of ordinary skill in the art, the demodulation processgenerally is somewhat the reverse of the modulation process andgenerally involves making best guess or maximum likelihood estimationsof the originally transmitted information given that an electromagneticsignal or physical phenomena is received that may have been corrupted byvarious factors including, but not limited to, noise. In general, TMTSdownstream radio frequency (RF) interface 554 carries signals that havebeen modulated for transmitting information downstream over an RFnetwork. TMTS upstream radio frequency (RF) interface 555 generallycarries signals that have to be demodulated to recover upstreaminformation from an RF network. Although the preferred embodiments ofthe present invention generally use quadrature amplitude modulation(QAM), one skilled in the art will be aware of other possible modulationtechniques. Furthermore, “Digital Communications, Fourth Edition” byJohn G. Proakis and “Digital Communications: Fundamentals andApplications, Second Edition” by Bernard Sklar are two common books ondigital communications that describe at least some of the knownmodulation techniques. These two books by John G. Proakis and BernardSklar are incorporated by reference in their entirety herein.

Tables 1, 2, 3 and 4 generally show the transmission parameters used inthe preferred embodiments of the present invention. One skilled in theart will be aware that other transmission characteristics and parameterscould be used for alternative embodiments of the present invention.Table 1 specifies at least some of the preferred transmission parametersfor downstream output from a TMTS. In addition, Table 2 specifies atleast some of the preferred transmission parameters for downstream inputinto a cTM. Also, Table 3 specifies at least some of the preferredtransmission parameters for upstream output from a cTM. Finally, Table 4specifies at least some of the preferred transmission parameters forupstream input to a TMTS.

Furthermore, one skilled in the art will be aware that the concepts ofthe embodiments of the present invention could be used in differentfrequency ranges using optional frequency upconverters and/ordownconverters. Therefore, although the preferred embodiments of thepresent invention may be designed to preferably work within thespecified frequency ranges, the scope of the concepts of the presentinvention is also intended to include all variations of the presentinvention that generally involve frequency shifting the operationalrange of the upstream and/or downstream channels in a cable distributionnetwork. Frequency shifting signals using upconverters and/ordownconverters is known to one of ordinary skill in the art of cablenetworks.

TABLE 1 Downstream output from TMTS Parameter Value Channel CenterFrequency 54 MHz to 857 MHz ±30 kHz (fc) Level Adjustable over the range50 to 61 dBmV Modulation Type 64 QAM and 256 QAM Symbol Rate (nominal) 64 QAM 5.056941 Msym/sec 256 QAM 5.360537 Msym/sec Nominal ChannelSpacing 6 MHz Frequency Response  64 QAM ~18% Square Root Raised CosineShaping 256 QAM ~12% Square Root Raised Cosine Shaping Output Impedance75 ohms Output Return Loss >14 dB within an output channel up to 750MHz; >13 dB in an output channel above 750 MHz Connector F connector per[IPS-SP-406] ±30 kHz includes an allowance of 25 kHz for the largest FCCfrequency offset normally built into upconverters.

TABLE 2 Downstream input to cTM Parameter Value Center Frequency (fc) 54MHz to 857 MHz ±30 kHz Level −5 dBmV to +15 dBmV Modulation Type 64 QAMand 256 QAM Symbol Rate (nominal)  64 QAM 5.056941 Msym/sec 256 QAM5.360537 Msym/sec Bandwidth  64 QAM 6 MHz with ~18% Square Root RaisedCosine Shaping 256 QAM 6 MHz with ~12% Square Root Raised Cosine ShapingTotal Input Power <30 dBmV (40-900 MHz) Input (load) Impedance 75 ohmsInput Return Loss >6 dB 54-860 MHz Connector F connector per[IPS-SP-406] (common with the output

TABLE 3 Upstream output from cTM Parameter Value Channel CenterFrequency (fc) Sub-split 5 MHz to 42 MHz Data-split 54 MHz to 246 MHzNumber of Channels Up to 3 Nominal Channel Spacing 6 MHz Channelcomposition Up to 14 independently modulated tones Tone Modulation TypeQPSK, 16 QAM, 64 QAM or 256 QAM Symbol Rate (nominal) 337500 symbols/sTone Level Adjustable in 2 dB steps over a range of −1 dBmV to +49 dBmVper tone (+ 10.5 dBmV to +60.5 dBmV per fully loaded channel, i.e. all14 tones present) Tone Frequency Response 25% Square Root Raised CosineShaping Occupied Bandwidth per Tone 421.875 kHz Occupied Bandwidth5.90625 MHz per Channel Output Impedance 75 ohms Output Return Loss >14dB Connector F connector per [IPS-SP-406]

TABLE 4 Upstream input to TMTS Parameter Value Channel Center Frequency(fc) Subsplit 5 MHz to 42 MHz Data-split 54 MHz to 246 MHz Tone nominallevel +20 dBmV Tone Modulation Type QPSK, 16 QAM, 64 QAM or 256 QAMSymbol Rate (nominal) 337500 symbols/s Tone Bandwidth 421.875 kHz with25% Square Root Raised Cosine Shaping Total Input Power (5-246 MHz) <30dBmV Input (load) Impedance 75 ohms Input Return Loss >6 dB 5-246 MHzConnector F connector per [IPS-SP-406]

Generally, the downstream signals associated with TMTS 215 may or maynot be combined in downstream RF combiner 556 with other downstream RFsignals from applications such as, but not limited to, analog video,digital video, DOCSIS data, and/or cable telephony. Upstream RF splitter557 may split the upstream signals for TMTS 215 from upstream signalsfor other applications such as, but not limited to, analog video,digital video, DOCSIS data, and/or cable telephony. Also, the downstreamRF combiner 556 and upstream RF splitter 557 might be used to carry thecommunications for multiple transport modem termination systems, such asTMTS 215, over a cable transmission (CT) network 105. The signals usedin communication between a TMTS 215 and at least one client transportmodem (cTM) 265 generally might be treated like any other RF signals forvarious applications that generally are multiplexed into cabletransmission (CT) network 105 based upon 6 MHz frequency channels.

If cable transmission (CT) network 105 is a hybrid fiber-coax (HFC)network, then the transport network 560 may include transmitter 561receiver 562 as optical/electrical (O/E) interfaces that convert the RFsignals between coaxial cable and fiber optical lines. In addition,transport combiner 563 may handle combining the two directions ofoptical signals as well as other potential data streams forcommunication over at least one fiber using techniques such as, but notlimited to, wavelength-division multiplexing (WDM). Thus, in a preferredembodiment of the present invention using HFC as at least part of cabletransmission (CT) network 105, transport media 565 may be fiber opticalcommunication lines.

FIG. 5 b generally shows the continuation of cable transmission (CT)network 105, transport network 560, and transport media 565 in providingconnectivity between TMTS 215 and at least one client transport modem(cTM) 265. In a preferred embodiment of the present invention thatutilizes fiber optic lines as at least part of transport network 560,transport splitter 567 may provide wavelength division multiplexing(WDM) and demultiplexing to separate the signals carried in the upstreamand downstream directions and possibly to multiplex other signals forother applications into the same at least one fiber. If transportnetwork 560 is a fiber network and cable transmission (CT) network 105is a hybrid fiber-coax network, then at least one distribution node 568may comprise optical/electrical interfaces to convert between a fibertransport network 560 and a coaxial cable distribution network 570. Ingeneral, there may be a distribution media interface 572 anddistribution media 574 that provide connectivity between at least oneclient transport modem (cTM) 265 and distribution node 568.

A client transport modem (cTM) 265 generally comprises a cabletransmission physical (PHY) transceiver (TX/RX) 165 as well as aremote-side network physical (PHY) transceiver (TX/RX) 275. In addition,a client transport modem (cTM) 265 comprises cable transmission (CT)physical (PHY) control (CTRL) 577 and system control 579. In general, CTPHY control 577 is concerned with handling bandwidth allocations incable transmission (CT) network 105, and system control 579 generally isconcerned with cTM management and/or configuration.

In the preferred embodiment of the present invention a client transportmodem (cTM) 265 generally interfaces with at least one subscriberphysical (PHY) interface network 580. Interfaces such as interface 285in FIG. 2 b may comprise a cable transport modem (cTM) 802.3 interface581 and/or a cTM circuit emulation service (CES) interface 582 in FIG. 5b. Thus, a cTM may have multiple interfaces to different remote-sidenetworks, and the interfaces may use different interface types and/ortechnologies. Also, a cTM 265 may have a cTM control interface 583 thatis used to allow at least one provisioning terminal 585 to performvarious tasks such as, but not limited to, configuration, control,operations, administration, and/or maintenance. In the preferredembodiment of the present invention, the cTM control interface 583 mayuse ethernet/802.3, though other interface types and technologies couldbe used. Also, cTM control interface 583 could use a separate interfacefrom interfaces used to connect to remote-side networks such assubscriber local area network 595. Based on various policy decisions andcriteria, such as but not limited to security, the cTM control interface583 may be carried over the same communications medium that connects tovarious remote-side networks or it may be carried over separatecommunications medium from that used in connecting to variousremote-side networks. In the preferred embodiment of the presentinvention, the cTM control interface 583 is carried in a separate802.3/ethernet medium for security.

Also, FIG. 5 b shows client transport modem (cTM) 265 being connectedover cTM circuit emulation service (CES) interface 582 to anotherremote-side network, the subscriber telephony network 596. Many remoteor subscriber locations have legacy equipment and applications that usevarious interfaces commonly found in connections to the PSTN. Thepreferred embodiments of the present invention allow connection of thesetypes of interfaces to the client transport modem (cTM) 265. Somenon-limiting examples of these interfaces are analog POTS lines as wellas various digital interfaces generally supporting N×56 and N×64 (whereN is any positive integer). The digital interfaces may have a pluralityof DS0s multiplexed into a larger stream of data using theplesiochronous digital hierarchy (PDH) and/or the synchronous digitalhierarchy (PDH). In the preferred embodiments of the present invention,cTM CES interface 582 is a Ti line, which is part of the plesiochronousdigital hierarchy (PDH).

Protocol Models

FIG. 6 shows more detail of a preferred embodiment of a transport modemtermination system (TMTS) 215 and/or a client transport modem (cTM) 265.In general, for various tasks such as, but not limited to,configuration, management, operations, administration, and/ormaintenance, a TMTS 215 and/or a cTM 265 generally may have a capabilityof system control 219 and/or 579, respectively. In general, the systemcontrol 219 and/or 579 may have at least one cable transmission (CT)physical (PHY) transceiver (TX/RX) 115 and/or 165 as well as at leastone interface for connecting to central-side and/or remote-side networkswith ethernet/802.3 physical (PHY) transceiver 225 and/or 275 being theat least one type of connection to the central-side and/or remote-sidenetworks in the preferred embodiment of the present invention. At leastone cable transmission (CT) physical (PHY) transceiver (TX/RX) 115and/or 165 generally is connected to at least one cable transmission(CT) network 105. Also, in the preferred embodiment of the presentinvention at least one ethernet/802.3 physical (PHY) transceiver 225and/or 275 is connected to at least one ethernet/802.3 media 605.

In general, a single instance of a 802.3/ethernet media access control(MAC) algorithm could be used for both the 802.3 physical (PHY)transceiver (TX/RX) 225 and/or 275 as well as the cable transmission(CT) physical (PHY) transceiver (TX/RX) 115 and/or 165. In otherembodiments multiple instances of a medium access control (MAC)algorithm may be used. In general, ethernet/802.3 uses a carrier sensemultiple access with collision detection (CSMA/CD) MAC algorithm. Eachinstance of the algorithm generally is responsible for handling thecarrier sensing, collision detection, and/or back-off behavior of in oneMAC collision domain. The details of the 802.3 MAC are further definedin IEEE standard 802.3-2000, “Part 3: Carrier sense multiple access withcollision detection (CSMA/CD) access method and physical layer”, whichwas published in 2000, and is incorporated by reference in its entiretyherein.

The preferred embodiment of the present invention generally functions asa physical layer repeater between at least one 802.3 media 605 and atleast one cable transmission (CT) network 105. Although repeaters maysupport a particular MAC algorithm for management and control purposes,generally repeaters do not break up a network into different collisiondomains and/or into different layer three sub-networks. However, oneskilled in the art will be aware that other embodiments are possible fordevices such as, but not limited to, bridges, switches, routers, and/orgateways. These other embodiments may have multiple instances of thesame and/or different MAC algorithms.

Furthermore, the CSMA/CD MAC algorithm as well as the physical layersignals that generally are considered part of the ethernet/802.3specification may be used to carry different frame types. In thepreferred embodiment of the present invention, because of thewide-spread availability of Internet Protocol (IP) technology, thesystem control 219 for TMTS 215 and/or the system control 579 for cTM265 generally may use IP for various tasks such as, but not limited to,configuration, management, operations, administration, and/ormaintenance. On ethernet/802.3 networks, IP datagrams commonly arecarried in Digital-Intel-Xerox (DIX) 2.0 or ethernet_II frames. However,other frame types may be used to carry IP datagrams including, but notlimited to, 802.3 frames with 802.2 logical link control (LLC) and asub-network access protocol (SNAP). Thus, 802.2 LLC/DIX 615 handles thecorrect frame type information for the IP datagrams communicated toand/or from the system control 219 and/or 579 of TMTS 215 and/or cTM265, respectively. Often network devices using the internet protocol(IP) are configurable for 802.2 LLC and/or ethernet_II frame types.

In general, for communications with IP devices a mapping should existbetween logical network layer addresses (such as IP addresses) andhardware, data link, or MAC layer addresses (such as ethernet/802.3addresses). One protocol for dynamically determining these mappingsbetween IP addresses and ethernet/802.3 addresses on broadcast media isthe address resolution protocol (ARP). ARP is commonly used in IPdevices that are connected to broadcast media such as ethernet/802.3media. Thus, the preferred embodiments of the present inventiongenerally support ARP 620 to allow tasks such as, but not limited to,configuration, management, operations, administration, and/ormaintenance of TMTS 215 and/or cTM 265.

In the preferred embodiments of the present invention, TMTS 215 and/orcTM 265 generally support management and/or configuration as IP devices.Thus, system control 219 and/or 579 generally has an IP layer 625 thatmay also optionally include support for ICMP. The internet controlmessage protocol (ICMP) is commonly used for simple diagnostic taskssuch as, but not limited to, echo requests and replies used in packetinternet groper (PING) programs. Generally, various transport layerprotocols such as, but not limited to, the user datagram protocol (UDP)630 are carried within IP datagrams. UDP is a connectionless datagramprotocol that is used in some basic functions in the TCP/IP(Transmission Control Protocol/Internet Protocol) suite. Generally, UDP630 supports the dynamic host configuration protocol (DHCP) 635, whichis an extension to the bootstrap protocol (BOOTP), the simple networkmanagement protocol (SNMP) 640, the trivial file transfer protocol(TFTP) 645, as well as many other protocols within the TCP/IP suite.

DHCP 635 is commonly used in IP devices to allow dynamic assignment ofIP addresses to devices such as TMTS 215 and/or cTM 265. SNMP 640generally supports “sets” to allow a network management system to assignvalues on the network devices, “gets” to allow a network managementsystem to retrieve values from network devices, and/or “traps” to allownetwork devices to information a network management system of alarmconditions and events. TFTP 645 might be used to load a configurationfrom a file onto a network device, to save off a configuration of anetwork device to a file, and/or to load new code or program softwareonto a network device. These protocols of DHCP 635, SNMP 640, and TFTP645 may be used in the preferred embodiment for control processes 650 insystem control 219 and/or 579 of TMTS 219 and/or cTM 265, respectively.

Furthermore, one skilled in the art will be aware that many otherinterfaces are possible for tasks such as, but not limited to,configuration, management, operations, administration, and/ormaintenance of TMTS 215 and/or cTM 265. For example, the system control219 or 579 in TMTS 215 and/or cTM 265 may support the transmissioncontrol protocol (TCP) instead of or in addition to UDP 630. With TCP,control processes 650 could use other TCP/IP suite protocols such as,but not limited to, the file transfer protocol (FTP), the hyper texttransfer protocol (HTTP), and the telnet protocol. One skilled in theart will be aware that other networking devices have used FTP for filetransfer, HTTP for web browser user interfaces, and telnet for terminaluser interfaces. Also, other common use interfaces on network equipmentinclude, but are not limited to, serial ports, such as RS-232 consoleinterfaces, as well as LCD (Liquid Crystal Display) and/or LED (LightEmitting Diode) command panels. Although the preferred embodiments ofthe present invention may use DHCP 635, SNMP 640, and/or TFTP 645, otherembodiments using these other types of interfaces are possible for taskssuch as, but not limited to, configuration, management, operations,administration, and/or maintenance of TMTS 215 and/or cTM 265.

In the preferred embodiments of the present invention, the local serverfacility 543 and/or the OA&M system 544 of FIG. 5 a as well as theprovisioning terminal 585 of FIG. 5 b are at least one host device 660that communicated with control processes 650 of TMTS 215 and/or cTM 265.In general, at least one host device 660 may be connected to 802.3 media605 through 802.3 physical (PHY) transceiver (TX/RX) 670. Host device660 may have an 802.3/ethernet (ENET) media access control (MAC) layer675, an 802.2 LLC/DIX layer 680, and higher layer protocols 685.Although FIG. 6 shows host device 660 directly connected to the same802.3 media 605 as TMTS 215 or cTM 265, in general there may be any typeof connectivity between host device 660 and TMTS 215 and/or cTM 265.This connectivity may include networking devices such as, but notlimited to, repeaters, bridges, switches, routers, and/or gateways.Furthermore, host device 660 does not necessarily have to have the sametype of MAC interface as TMTS 215 and/or cTM 265. Instead, host device660 generally is any type of IP host that has some type of connectivityto TMTS 215 and/or cTM 265 and that supports the proper IP protocolsand/or applications for tasks such as, but not limited to,configuration, management, operations, administration, and/ormaintenance.

FIG. 7 shows a more detailed breakdown of how TMTS 215 and cTM 265 mightprovide communication over cable transmission network 105. The preferredembodiments of the present invention might be used in a networkgenerally divided at point 740 into a service-provider-side (orcentral-side) of the network 742 as well as a subscriber-side,customer-side, or remote-side of the network 744. In general, TMTS 215would be more towards the central-side or service-provider-side of thenetwork 742 relative to cTM 265, which would be more towards thesubscriber-side, customer-side, or remote-side of the network 744relative to the TMTS 215. As was shown in FIGS. 5 a and 5 b, and isshown again in FIG. 7, TMTS 215 may comprise a cable transmission (CT)physical (PHY) transceiver (TX/RX) 115, an ethernet/802.3 physical (PHY)transceiver (TX/RX) 225, and a cable transmission (CT) physical (PHY)control 217. Also, cTM 265 may comprise a cable transmission (CT)physical (PHY) transceiver (TX/RX) 165, an ethernet/802.3 physical (PHY)transceiver (TX/RX) 275, and a cable transmission (CT) physical (PHY)control 577.

In the preferred embodiment of the present invention, TMTS 215 and cTM265 generally provide layer one, physical level repeater service betweenethernet/802.3 physical (PHY) transceiver (TX/RX) 225 and ethernet/802.3physical (PHY) transceiver (TX/RX) 275. Furthermore, cable transmission(CT) physical (PHY) control 217 in TMTS 215 generally communicates withcable transmission (CT) physical (PHY) control 577 in cTM 265 toallocate and/or assign bandwidth. In addition to allocating and/orassigning bandwidth, cable transmission (CT) physical control 217 andcable transmission (CT) physical control 577 generally may includemechanisms to request and release bandwidth as well as to inform thecorresponding cable transmission (CT) physical (PHY) control of thebandwidth allocations. Also, cable transmission (CT) physical control217 and cable transmission (CT) physical control 577 generally maycommunicate to negotiate cTM radio frequency (RF) power levels so thatthe TMTS receives an appropriate signal level.

In the preferred embodiments of the present invention, the TMTS 215 andthe cTM 265 generally are transparent to ethernet/802.3 framescommunicated between ethernet/802.3 physical (PHY) transceiver (TX/RX)225 and ethernet/802.3 physical (PHY) transceiver 275. To maintain thistransparency, the communication between cable transmission (CT) physical(PHY) control 217 and cable transmission (CT) physical (PHY) control 577generally do not significantly modify and/or disturb the ethernet framescommunicated between 802.3/ethernet physical (PHY) transceiver (TX/RX)225 and 802.3/ethernet physical (PHY) transceiver (TX/RX) 275. There aremany possible ways of communicating between cable transmission (CT)physical (PHY) control 217 and cable transmission (CT) physical (PHY)control 577 of TMTS 215 and cTM 265, respectively, while stillmaintaining transparency for the 802.3 physical transceivers 225 and/or275. In the preferred embodiments of the present invention, the trafficbetween cable transmission (CT) physical (PHY) control 217 and 577 ofTMTS 215 and cTM 265, respectively, is multiplexed into the same datastream with 802.3/ethernet traffic between 802.3 physical (PHY)transceivers 225 and 275 of TMTS 215 and cTM 265, respectively. However,the control traffic generally uses a different frame than standardethernet/802.3 traffic.

Ethernet/802.3 frames generally begin with seven octets of preamblefollowed by a start frame delimiter of 10101011 binary or ABhexadecimal. (In reality ethernet DIX 2.0 has an eight octet preamble,and IEEE 802.3 has a seven octet preamble followed by a start framedelimiter (SFD). In either case, these initial eight octets aregenerally the same for both ethernet DIX 2.0 and IEEE 802.3.) Todifferentiate control frames between cable transmission (CT) physical(PHY) control 217 and 577 from ethernet frames between 802.3 physical(PHY) transceivers (TX/RX) 225 and 275, a different value for the eighthoctet (i.e., the start frame delimiter) may be used on the controlframes. Because most devices with ethernet/802.3 interfaces wouldconsider a frame with a start frame delimiter (SFD) to be in error,these control frames generally are not propagated through 802.3 physical(PHY) transceivers (TX/RX) 225 and/or 275. This solution offers theadvantage of the control frames that communicate bandwidth allocationsbeing generally inaccessible to devices on directly connected 802.3media. This lack of direct accessibility to the control frames mayprovide some security for communications about bandwidth allocations,which may be related to various billing policies. Because cabletransmission (CT) physical (PHY) control 217 and 577 generally does notgenerate 802.3 or ethernet frames in the preferred embodiment of thepresent invention, FIG. 7 shows cable transmission (CT) physical (PHY)control 217 and 577 generally connected to cable transmission (CT)physical (PHY) transceivers (TX/RX) 115 and 165, respectively, andgenerally not connected to 802.3/ethernet physical (PHY) transceivers(TX/RX) 225 and 275, respectively.

As shown in FIG. 7, ethernet/802.3 physical (PHY) transceiver (TX/RX)225 in TMTS 215 generally is connected to 802.3/ethernet media 745,which is further connected to at least one device with an ethernetinterface 750. Device with ethernet interface 750 may further comprisean 802.3/ethernet physical (PHY) transceiver (TX/RX) 755, an802.3/ethernet medium access control layer 756, as well as other higherlayer protocols 757. Also, ethernet/802.3 physical (PHY) transceiver(TX/RX) 275 in cTM 265 generally is connected to 802.3/ethernet media785, which is further connected to at least one device with an ethernetinterface 790. Device with ethernet interface 790 may further comprisean 802.3/ethernet physical (PHY) transceiver (TX/RX) 795, an802.3/ethernet medium access control layer 796, as well as other higherlayer protocols 797.

In general, the preferred embodiments of the present invention providetransparent physical layer repeater capability that may carryinformation between device with ethernet interface 750 and device withethernet interface 790. As a non-limiting example, device with ethernetinterface 750 may have information from a higher layer protocol such as,but not limited to, an IP datagram. In FIG. 7, this IP datagram isformed in the higher layer protocols block 757 and is passed down to802.3/ethernet MAC layer 756, which adds data link information to forman ethernet frame. Then 802.3 physical (PHY) transceiver (TX/RX) 755handles generating the proper electromagnetic signals to propagate theinformation over 802.3/ethernet media 745. In the preferred embodimentsof the present invention, TMTS 215 functions as a repeater that copiesbits (or other forms of information) received from 802.3/ethernet media745 by 802.3/ethernet physical (PHY) transceiver (TX/RX) 225. The bitsare copied over to cable transmission (CT) physical (PHY) transceiver(TX/RX) 115, which generates the proper signals to communicate theinformation over cable transmission network 105. (Note: in someembodiments some portions of the signal generation may be performedexternally to the TMTS 215 as in at least one external QAM modulator552.)

After propagating through cable transmission (CT) network 105, the bits(or other forms of information) are received in cable transmission (CT)physical (PHY) transceiver (TX/RX) 165 of cTM 265. In the preferredembodiments of the present invention, cTM 265 functions as a repeaterthat copies bits (or other forms of information) received from cabletransmission network 105 by cable transmission (CT) physical (PHY)transceiver (TX/RX) 165. The bits are copied over to 802.3/ethernetphysical (PHY) transceiver (TX/RX) 275, which generates the propersignals to communicate the information over 802.3/ethernet media 785.

In device with ethernet interface 790, 802.3/ethernet physical (PHY)transceiver (TX/RX) 795 receives the electromagnetic signals on802.3/ethernet media 785 and recovers the bits (or other forms ofinformation) from the electromagnetic signals. Next, 802.3/ethernetmedia access control (MAC) 796 generally checks the ethernet/802.3framing and verifies the frame check sequence (FCS) or cyclic redundancycode (CRC). Finally, the IP datagram is passed up to higher layerprotocols 797. Generally, a reverse process is followed forcommunications in the opposite direction.

Furthermore, it is to be understood that embodiments of the presentinvention are capable of providing similar connectivity over cabletransmission (CT) network 105 to devices (such as device with ethernetinterface 750 and device with ethernet interface 790), which may bedirectly connected to 802.3/ethernet media 745 and/or 785 as well asother devices that are not directly connected to 802.3/ethernet media745 and/or 785. Thus, other devices which are indirectly connected to802.3/ethernet media through other media, links, and/or networkingdevices may also utilize the connectivity provided by the preferredembodiments of the present invention.

In the preferred embodiments of the present invention, TMTS 215 can bethought of as providing level one, physical layer repeater servicebetween 802.3/ethernet physical (PHY) transceiver (TX/RX) 225 and cabletransmission (CT) physical (PHY) transceiver (TX/RX) 115. Also in thepreferred embodiments of the present invention, cTM 265 can be thoughtof as providing level one, physical layer repeater service between802.3/ethernet physical (PHY) transceiver (TX/RX) 275 and cabletransmission (CT) physical (PHY) transceiver (TX/RX) 165. In addition inthe preferred embodiments of the present invention, TMTS 215 and cTM 265together can be thought of as providing level one, physical layerrepeater service between 802.3/ethernet physical (PHY) transceiver(TX/RX) 225 and 802.3/ethernet physical (PHY) transceiver (TX/RX) 275.In providing level one, physical layer repeater service between802.3/ethernet physical (PHY) transceiver (TX/RX) 225 and 802.3/ethernetphysical (PHY) transceiver (TX/RX) 275, TMTS 215 and cTM 265 each may bethought of as half-repeaters of a repeater pair.

In general, networking devices connecting local area networks (or LANssuch as, but not limited to, ethernet/802.3 media 745 and 785) over awide-area network (or WAN such as, but not limited to, cabletransmission network 105) may be viewed using at least two abstractionsor models. First, the two devices at each end of the WAN may be viewedas independent networking devices each acting as a repeater, bridge,switch, router, gateway, or other type of networking device connectingthe LAN and the WAN. Alternatively, a pair of networking devices on eachend of a WAN could be viewed based on each networking device providingone half of the service provided over the WAN. Thus, each networkingdevice at the end of a WAN could be thought of as a half-repeater,half-bridge, half-switch, half-router, half-gateway, etc. for a pair ofnetworking devices providing connectivity across a WAN. In addition, oneskilled in the art will be aware that the networking devices on each endof a connection may actually perform according to different forwardingconstructs or models (such as, but not limited to, repeater, bridge,switch, router, and/or gateway). Thus, one skilled in the art will beaware that one of the networking devices (either the TMTS 215 or a cTM265) connected to cable transmission network may provide services suchas, but not limited to, repeater, bridge, switch, router, and/or gatewaywhile the other networking device (either a cTM 265 or the TMTS 215,respectively) may provide the same or different services such as, butnot limited to, repeater, bridge, switch, router, and/or gateway.Furthermore, each networking device could provide different services orforwarding constructs for different protocols.

Therefore, even though the preferred embodiments of the presentinvention have a repeater service or forwarding construct for both aTMTS 215 and a cTM 265 as well as a TMTS 215 and a cTM 265 jointly, oneskilled in the art will be aware that other embodiments of the presentinvention are possible in which the forwarding construct for a TMTS 215and/or a cTM may be independently chosen. Furthermore, the forwardingconstruct could be different for each client transport modem 265, 266,267, and 268 connected to the same TMTS 215. Also, transport modemtermination systems 215 may have different forwarding behavior orforwarding constructs for each port. In addition, multiple TMTS 215devices might utilize different forwarding constructs but still beconnected to the same cable transmission network 105. Also, one skilledin the art will be aware of hybrid forwarding constructs in addition tothe general layer one repeater service, layer two bridge service, and/orlayer three routing service. Any hybrid type of forwarding constructalso might be used as alternative embodiments of the present invention.Therefore, one skilled in the art will be aware that alternativeembodiments exist utilizing other forwarding constructs in addition tothe layer one, repeater service of the preferred embodiment of thepresent invention.

FIG. 7 further shows an 802.3/ethernet media independent interface (MII)799 as a dashed line intersecting connections to various 802.3/ethernetphysical layer interfaces or transceivers (755, 225, 275, and 795). Ingeneral, the IEEE 802.3 standards defined a media independent interfacefor 100 Mbps ethernet and a Gigabit media independent interface (GMII)for 1000 Mbps ethernet. References in the figures and description to MIIand/or GMII are meant to include both MII and GMII. Generally, the MIIand GMII interfaces allow 802.3 interfaces to be made that can beinterfaced with different physical cables. As a non-limiting example,100BaseT4, 100BaseTX, and 1000BaseFX are three different types ofphysical cables/optical lines that can be used in the IEEE 802.3ethernet standards covering 100 Mbps or fast ethernet. 100BaseTX isdesigned for twisted pair cables, whereas 100BaseFX is designed forfiber optic cables. The media independent interface (MII) provides astandard interface for communicating with devices designed to form andinterpret the physical electrical and/or optical signals of differenttypes of media.

FIG. 8. shows a more detailed diagram for connecting ethernet devicesthrough a transport modem termination system (TMTS) 215 and a clienttransport modem (cTM) 265. FIG. 8 further divides the cable transmission(CT) physical (PHY) transceiver (TX/RX) 115 and 165. TMTS 215 comprisesCT PHY 115, which further comprises signaling medium dependent (SMD)sublayer 816, physical coding sublayer (PCS) 817, inverse multiplexsublayer (IMS) 818, and frame management sublayer (FMS) 819. FMS 819connects to 802.3/ethernet physical transceiver 225 through802.3/ethernet media interface (MII) 799. SMD sublayer 816 communicatesthrough cable transmission (CT) network 105 across 802.3/ethernet mediadependent interface (MDI) 835.

Also client transport modem 265 has a cable transmission physicaltransceiver 165 that comprises signaling medium dependent (SMD) sublayer866, physical coding sublayer (PCS) 867, inverse multiplex sublayer(IMS) 868, and frame management sublayer (FMS) 869. SMD sublayer 866communicates through cable transmission network 105 across 802.3 mediadependent interface (MDI) 835. FMS 869 provides an 802.3 mediaindependent interface (MII) 799, which may be connected to an 802.3ethernet physical transceiver 275.

In general, FMS 819 and 869 provide management functions that allowcontrol traffic to be combined with and separated from data traffic. Aframe management sublayer (such as FMS 819 and/or 869) may support aplurality of 802.X interfaces. Each active 802.X port of FMS 869 inclient transport modem 265 generally has a one-to-one relationship withan associated active 802.X port in a transport modem termination system215. Generally FMS 819 within TMTS 215 has similar behavior to FMS 869in cTM 265. However, as TMTS 215 generally is a concentrator that maysupport a plurality of client transport modems, such as cTM 265, FMS 819of TMTS 215 usually has more 802.X interfaces than FMS 869 of cTM 265.

The inverse multiplex sublayer of IMS 818 and IMS 868 generally isresponsible for multiplexing and inverse multiplexing data streams ofFMS 819 and 869 across multiple frequency-division multiplexed (FDM)carriers. The asymmetrical differences in cable transmission networksbetween one-to-many downstream broadcast and many-to-one upstreamtransmission generally lead to different techniques for downstreammultiplexing than the techniques for upstream multiplexing. In thepreferred embodiment of the present invention downstream multiplexingutilizes streams of MPEG (Moving Picture Experts Group) frames on sharedfrequencies of relatively larger bandwidth allocations, while upstreammultiplexing utilizes non-shared frequencies of relatively smallerbandwidth allocations. Even though the upstream and downstream bandwidthallocation techniques of the inverse multiplexing sublayer (IMS) aredifferent, the preferred embodiments of the present invention are stillcapable of providing symmetrical upstream and downstream data rates (aswell as asymmetrical data rates). Furthermore, the inverse multiplexingsublayer (IMS) splits the incoming sequential octets of FMS data flows(i.e., flows of data from and/or to FMS ports) for parallel transmissionacross a cable transmission network utilizing a plurality of frequencybands in parallel. This parallel transmission of data flows will tend tohave lower latency than serial transmission.

The physical coding sublayer (such as PCS 817 and 867) generally isresponsible for handling forward error correction (FEC) and quadratureamplitude modulation (QAM) coding and decoding of the informationcommunicated between IMS sublayer peer entities (such as IMS 818 and IMS868). The signaling medium dependent (SMD) sublayer (such as the SMDpeer entities 816 and 866) generally is responsible for communicatingthe encoded and modulated information from the physical coding sublayeronto a cable transmission network 105 at the proper frequency ranges andin the proper optical and/or electrical carrier waves.

FIG. 9 shows the open systems interconnect (OSI) seven-layer model,which is known to one of skill in the art, as well as the relationshipof the OSI model to the physical layer specification of the preferredembodiments of the present invention and to some portions of the IEEE802.X standards. In OSI terminology corresponding layers (such as thelayer 3 Internet Protocol) of two communicating devices (such as IPhosts) are known as peer entities. The OSI model comprises the level 1physical layer 901, the level 2 data link layer 902, the level 3 networklayer 903, the level 4 transport layer 904, the level 5 session layer905, the level 6 presentation layer 906, and the level 7 applicationlayer 907. The preferred embodiments of the present invention generallyoperate over communication media that function as cable transmissionnetwork 915. Although cable transmission network 915 certainly compriseshybrid fiber-coax (HFC) cable plants, CT network 915 more generally alsocomprises all coax and all fiber transmission plants. Furthermore, cabletransmission network 915 even more generally comprises any communicationmedium using frequency-division multiplexing (FDM) and/or the opticalvariation of frequency division multiplexing known as wavelengthdivision multiplexing (WDM).

The cable transmission network 915 communicates information across amedia dependent interface (MDI) 925 with cable transmission physicallayer 935. FIG. 9 shows that cable transmission physical layer 935 isassociated with the physical layer 901 of the OSI model. Similarly toFIG. 8, cable transmission PHY 935 is shown in FIG. 9 with the foursublayers of the signaling medium dependent sublayer (SMD) 945, physicalcoding sublayer (PCS) 955, inverse multiplex sublayer (IMS) 965, andframe management sublayer (FMS) 975. The SMD 945, PCS 955, IMS 965, andFMS 975 sublayers form a user plane that generally is concerned withcommunicating user data. In addition, cable transmission PHY control 985provides functions generally associated with management and/or controlof communications through cable transmission physical layer 935 and thecorresponding four sublayers (945, 955, 965, and 975).

FIG. 9 further shows how data link layer 902 is divided into mediumaccess control sublayer (MAC) 998 and logical link control sublayer(LLC) 999 that are generally described in the IEEE 802 standards. IEEE802.3 generally describes the carrier sense multiple access withcollision detection (CSMA/CD) medium access control (MAC) protocol,while IEEE 802.2 generally describes the logical link control (LLC)protocol. Cable transmission physical layer 935 generally has a mediaindependent interface (MII) 995 that provides connectivity between FMS975 and an IEEE 802.3 MAC. Furthermore, one skilled in the art will beaware that the OSI model as well as other communication models are onlyabstractions that are useful in describing the functionality, behavior,and/or interrelationships among various portions of communicationsystems and the corresponding protocols. Thus, portions of hardwareand/or software of actual networkable devices and the associatedprotocols may not perfectly match the abstractions of variouscommunication models. Often when multi-layer abstract models ofcommunication systems are mapped onto actual hardware and/or softwarethe dividing line between one layer (or sublayer) and an adjacent layer(or sublayer) becomes somewhat blurred as to which hardware and/orsoftware elements are part of which abstract layer. Furthermore, it isoften efficient to used shared portions of hardware and/or software toimplement interfaces between the abstract layers. However, the abstractmodels are useful in describing the characteristics, behavior, and/orfunctionality of communication systems.

Much like peer entities of OSI protocol layers, there can also be peerentities of protocol sublayers. Thus, corresponding FMS, IMS, PCS,and/or SMD sublayers in communicating devices could be considered peerentities. Given this peer entity relationship, one of many alternativeembodiments of the present invention is shown in FIG. 10. TMTS 215 anddevice with ethernet interface 750 are shown again in FIG. 10 but thistime TMTS 215 transfers information with a client transport modemnetwork interface card (NIC) 1065. CTM NIC 1065 comprises a CT physicallayer transceiver (TX/RX) 1075 that is a peer entity of CT physicallayer transceiver 115 of TMTS 215. Also, cTM NIC 1065 further comprisesCT physical layer control 1077 that is a peer entity of CT physicallayer control 217 of TMTS 215. Also, cTM NIC 1065 comprises802.3/ethernet MAC 1079 that is a peer entity of 802.3/ethernet MAC 757in device with ethernet interface 750.

Client transport modem NIC 1065 is shown within device with cTM NIC1090, which further contains NIC driver software 1097 and higher layerprotocols 1099. If device with cTM NIC 1090 is a personal computer, thenNIC driver software 1097 might conform to one of the driverspecifications, such as but not limited to, NDIS (Network DriverInterface Specification), ODI (Open Data-Link Interface), and/or theClarkson packet drivers. Usually a network interface card plugs into abus card slot and then uses driver software to interface with higherlayer protocols. One skilled in the art will be aware that the cabletransmission physical layer of the preferred embodiment of the presentinvention could be implemented in any type of networkable device inaddition to PCs and workstations. Some non-limiting examples ofnetworkable devices include computers, gateways, routers, switches,bridges, and repeaters. Sometimes these devices have expansion cardbuses that could be used to interface to logic implementing the cabletransmission physical layer 1075 of the preferred embodiments of thepresent invention. Alternatively, the preferred embodiments of thepresent invention could be directly integrated into the base units ofnetworkable devices. FIG. 11 further expands cable transmission physicallayer 1075 (and the associated physical layer transceiver) into SMDsublayer 1166, PCS sublayer 1167, IMS sublayer 1168, and framemanagement sublayer 1169.

Frame Management Sublayer (FMS) Data Flows

FIG. 12 shows a system diagram using the physical layer of the preferredembodiment of the present invention for communication between atransport modem termination system and a client transport. The foursublayers (FMS 1202, IMS 1204, PCS 1206, and SMD 1208) are shown withindashed boxes. The upper portion of FIG. 12 shows downstreamcommunication from a TMTS to a cTM, while the lower portion of FIG. 12shows upstream communication from a cTM to a TMTS.

In the downstream communication ethernet/802 packets ingress into acable transmission physical layer of the preferred embodiments of thepresent invention at ethernet/802 ingress 1212, which performs aconversion from ethernet/802 packets to FMS frames. FMS frames are thencommunicated to downstream multiplexer 1214 which converts the octets inFMS frames to octets in MPEG frames. MPEG headers and MPEG forward errorcorrection (FEC) coding, which generally is a Reed-Solomon code,generally are added for communication to downstream modulator(s) 1216.The output of downstream modulator(s) 1216 is passed through radiofrequency (RF) transmitter (TX) 1218, which generates the electricaland/or optical signals in the proper frequencies. These signals arecommunicated over cable transmitter network 1220 into RF receiver (RX)1222. The incoming information in the electrical and/or optical signalsgenerally is recovered into the MPEG frames in downstream demodulator1224. The downstream MPEG frames are then passed to downstream inversemultiplexer 1226, which extracts the proper octets from MPEG frames torecover frame management sublayer (FMS) frames. The FMS frames then areconverted back to ethernet/802 frames and complete downstream conveyanceat ethernet/802 egress 1228.

Upstream communication of ethernet/802 packets ingress into a physicallayer of the preferred embodiments of the present invention atethernet/802 ingress 1248 which converts the ethernet/802 frames intoframe management sublayer (FMS) frames. The FMS frames are convertedinto blocks of data in preparation for forward error correction codingin upstream multiplexer 1246. These upstream blocks of data may carrythe octets of ethernet/802 frames over multiple carrier frequencies. Inthe preferred embodiment of the present invention a turbo product codeforward error correction technique is utilized on the upstream blocks ofdata. One skilled in the art will be aware of the techniques of turboproduct codes as well as alternative coding techniques for errordetection and/or forward error correction. Upstream modulator 1244modulates the information of the forward error correction blocks andpasses the resulting modulating information to RF transmitter 1242,which generates the electrical and/or optical signals in the properfrequency ranges for communication over cable transmission network 1220.The upstream electrical and/or optical signals are received in RFreceiver 1238. Upstream demodulator 1236 then handles recovering theforward error correction blocks of data. Also, upstream demodulator 1236converts the forward error correction blocks back to the original blocksof data that were prepared in upstream multiplexer 1246. The octets ofthe data blocks are placed back into the proper FMS frames in upstreaminverse multiplexer 1234. These FMS frames are then further convertedback to ethernet/802 frames and leave the physical layer at ethernet/802egress 1232.

FIG. 13 shows a more detailed diagram of the frame management sublayer(FMS). In FIG. 13 802.3/ethernet media 1302 is connected across mediaindependent interface (MII) and/or gigabit media independent interface(GMII) 1304 to frame management sublayer (FMS) 1306, which is furtherconnected to inverse multiplex sublayer (IMS) 1308. The connections ofFMS 1306 to 802.3/ethernet media 1302 are known as uplink ports 1through N (1312, 1314, 1316, and 1318). While the connections of FMS1306 leading to IMS 1308 generally are known as attachment ports 1through N (1322, 1324, 1326, and 1328). Each attachment port (1322,1324, 1326, and 1328) is connected to its own set of at least one framebuffer (1332, 1334, 1336, and 1338, respectively) that provides at leastpart of the interface between FMS 1306 and IMS 1308. Frame buffer(s)(1332, 1334, 1336, and 1338) provide bidirectional communication of FMSdata flows (1342, 1344, 1346, and 1348, respectively) between FMS 1306and IMS 1308. In general, each active FMS data flow of a framemanagement sublayer in one device is associated one-to-one with anactive data flow of a peer entity frame management sublayer in anotherdevice. Generally, each FMS data flow provides bi-directionalconnection-oriented communication between frame management sublayer peerentities in the associated devices. Thus, an FMS data flow generallyprovides bi-directional point-to-point connectivity between a pair ofFMS peer entities.

FIG. 13 further shows various control functions 1352, which comprise802.3/ethernet medium access control (MAC) interface 1354, cabletransmission physical layer control 1356, and system control 1358. CTPHY 1356 generally handles control of the cable transmission physicallayer, which includes the sublayers of FMS 1306 and IMS 1308 that areshown in FIG. 13. System control 1358 includes many of the networkmanagement, software download, and/or configuration setting filedownload and/or upload capabilities that generally utilize protocolsfrom the TCP/IP suite for administering network devices.

Basically the frame management layer (FMS) 1306 is responsible forframing ethernet data into the proper frames for communications usingthe preferred embodiments of the present invention. Furthermore, controlflows are communicated between cable transmission physical control 1356and a corresponding peer entity cable transmission physical control inanother device. These control flows are not part of the user data, andthus are not communicated through FMS 1306 to the uplink ports (1312,1314, 1316, and 1318) that carry information to 802.3/ethernet media1302. The control frames of control flows may be multiplexed with dataframes by utilizing different start frame delimiters to indicateethernet data frames and control frames.

FIG. 14 shows a general format for an 802.3/ethernet frame as is knownby one of ordinary skill in the art. In general, an ethernet framecomprises a preamble 1402 that is used to synchronize the transmitterand receiver in 802.3/ethernet media. After the preamble, start framedelimiter 1404 is used to indicate the beginning of the 802.3/ethernetframe. In IEEE 802.3 and ethernet, this start frame delimiter is the oneoctet value of 0xAB (in hexadecimal). Following the start framedelimiter (SFD) 1402, 802.3/ethernet frames generally have a header 1406that includes six octets of destination address, six octets of sourceaddress, and other information depending on whether the frame type isIEEE 802.3 raw, ethernet_II, IEEE 802.3 with an 802.2 LLC, or IEEE 802.3with an 802.2 LLC and a Sub-Network Access Protocol (SNAP). In addition,one skilled in the art will be aware of various techniques for taggingor labeling ethernet/802.3 frames, such as but not limited to,Multi-Protocol Label Switching (MPLS), Resilient Packet Ring (RPR),and/or Virtual LAN (VLAN). After the labeling or tagging information andthe 802.3/ethernet header 1406, data 1408 generally is carried in avariable length payload. At the end of 802.3/ethernet packets, a framecheck sum (FCS) 1410 error detecting code (usually using a cyclicredundancy check (CRC)) is computed.

To allow all the ethernet/802.3 frame types and various labeling and/ortagging protocols to be transparently communicated using the preferredembodiments of the present invention, the start frame delimiter is usedas a field for multiplexing control frames with ethernet/802.3 dataframes. Normally, ethernet/802.3 frames do not use the start framedelimiter (SFD) field 1404 for multiplexing because the SFD octet isresponsible for providing proper frame alignment in ethernet/802.3networks. FIG. 15 shows the frame format for control frames in thepreferred embodiment of the present invention. In some ways, controlframes are similar to ethernet II and 802.3 raw frames with a preamble1502, a start frame delimiter (SFD) 1504, a six octet destinationaddress 1505, a six octet source address 1506, a two octet length and/ortype field 1507, a variable length payload 1508 for carrying controlinformation, and a four octet frame check sequence (FCS) or cyclicredundancy code (CRC) 1510.

However, in comparing the prior art ethernet/802.3 data frame of FIG. 14with the control frame of FIG. 15 utilized in communication systemsusing the preferred embodiments of the present invention, the startframe delimiter fields 1404 and 1504 are different. For ethernet/802.3data frames in FIG. 14, the start frame delimiter has a value of 0xAB inhexadecimal, while for control frames in FIG. 15 the start framedelimiter has a value of 0xAE in hexadecimal. This difference in theoctet of the start frame delimiter (SFD) allows data frames and controlframes to be multiplexed together without affecting the transparency ofthe communication system to all types of ethernet/802.3 framevariations. Control frames transmitted by cable transmission physicalcontrol (such as 1356) are multiplexed with the data of an FMS data flow(such as 1342, 1344, 1346, and/or 1348) that is destined for the samelocation as the data of that FMS data flow.

In addition, FIG. 16 shows the FMS frames 1602 communicated between FMSpeer entities in a system utilizing the preferred embodiments of thepresent invention. In general, because of the one-to-one orpoint-to-point, non-shared relationship of connection-orientedcommunications between active FMS attachment ports and associated activepeer entity FMS attachment ports, bits may be continuously transmittedto maintain synchronization. In the absence of any data frames orcontrol frames to transmit, the system continuously communicates anoctet of 0x7E hexadecimal, which functions similarly to the continuouscommunication of HDLC (High-level Data-Link Control) flags in manypoint-to-point synchronous connections. Furthermore, as shown in FIG.16, the delimiter 1604 for an FMS frame 1602 is one octet of 0x00followed by six octets of 0x7E hexadecimal 1605. The frame delimiter ofan FMS frame 1602 is followed by a one octet start frame delimiter (SFD)1606 that contains the value 0xAB hexadecimal for ethernet/802.3 dataframes and that contains the value 0xAE hexadecimal for control framesas shown in FIG. 15. FMS frame 1602 generally has a frame trailer 1608and a payload 1610. When two FMS frames are transmitted immediatelyafter each other, only one octet of 0x00 and six octets of 0x7E 1605 areneeded between the two FMS frames. In other words, there is no need totransmit both a trailer 1608 for a first FMS frame 1602 and a startingdelimiter 1604 for a second FMS frame 1602 when the second FMS frame istransmitted immediately after the first FMS frame. Thus, when a secondFMS frame is transmitted immediately after a first FMS frame, either thetrailer 1608 of the first FMS frame or the starting delimiter 1604 ofthe second FMS frame may be omitted.

In general, the payload 1610 of an FMS frame 1602 generally may carry anethernet/802.3 frame or a control frame beginning with the SFD octets of0xAB and 0xAE, respectively, and continuing through the frame checksequence (FCS) 1410 or 1510. Because one hexadecimal octet (or aconsecutive sequence of a plurality of hexadecimal octets) with thevalue of 0x7E may appear in ethernet/802.3 and/or control frames, anoctet stuffing technique is used to ensure that the information in anFMS frame payload 1610 is communicated transparently and that the FMSframe 1602 boundaries can be detected by a starting FMS delimiter 1604and an FMS trailer 1608 (i.e., a trailing FMS delimiter). The FMSsublayer handles this process of framing ethernet and control framesusing the FMS frame delimiters of one octet of 0x00 followed by sixoctets of 0x7E. In addition, byte or octet stuffing allows a payloadcontaining octet or byte values that might cause misinterpretations ofstarting delimiter 1604 or trailing delimiter 1608 to be communicatedtransparently. Various techniques for byte, octet, and/or characterstuffing in byte-oriented protocols as well as bit stuffing inbit-oriented protocols are known by one of ordinary skill in the art,and one technique is described in Andrew S. Tanenbaum's Second and ThirdEditions of “Computer Networks”, which are both incorporated byreference in their entirety herein. Furthermore, the HDLC formattedframes communicated using an asynchronous, byte- or octet-orientedversion of the Point-to-Point Protocol (PPP) generally use anotheroctet-stuffing procedure to maintain transparency. This, octet stuffingprocedure is described in Internet Request For Comments (RFC) 1662,which is entitled “PPP in HDLC Framing” and is incorporated in itsentirety by reference herein.

In general, octet stuffing involves adding additional octets to a framewhenever a pattern in the frame might cause an ambiguity in a receivertrying to determine frame boundaries. For example, six payload octets of0x7E at 1612 in FIG. 16 could have an extra octet of 0x00 added as astuffed octet 1614. The additional stuffed octets generally increase thesize of the payload. One or more stuffed octets 1614 may be added to apayload to handle each situation where a receiver might have had someambiguity in determining correct frame boundaries based on the patternsin the payload data matching or overlapping with the bit patterns usedto specify frame boundaries.

FIG. 17 shows the relationships of inverse multiplex sublayer 1308 toframe management sublayer 1306 and physical coding sublayer 1710.Several of the items from FIG. 13 have been repeated including controlfunctions 1352, systems control 1358, CT PHY control 1356 as well as FMSdata flows 1 through N (1342, 1344, 1346, and 1348). The frame buffersbetween FMS 1306 and IMS 1308 have been omitted for simplicity of thediscussion of FIG. 17. Physical coding sublayer 1710 varies depending onwhether client transport modem modulation 1712 or transport modemtermination system modulation 1722 is being used. Client transport modemmodulation comprises a downstream demodulator 1714 that provides inputinto IMS 1308 and further comprises upstream modulator 1716 thatreceives the output of an inverse multiplex sublayer 1308. In contrastto the cTM modulation 1712, the TMTS modulation 1722 comprises upstreamdemodulator 1724 that provides input to an IMS 1308 and furthercomprises downstream modulator 1726 that receives input from IMS 1308.The IMS 1308 performs different multiplexing/demultiplexing functionsdepending on whether the direction of communication is upstream ordownstream. As discussed previously the downstream modulator 1726 of atransport modem termination system may include integrated QAMmodulators. Alternatively, the downstream MPEG packets and/or frames maybe communicated over an optional asynchronous serial interface (ASI)1732 to an external QAM modulator. One skilled in the art is aware ofmany mechanisms and devices that are commonly used in communicating MPEGframes over ASI interfaces to QAM modulators. Furthermore, because thedownstream communication of IMS 1308 utilizes MPEG streams that cancarry clock information, IMS 1308 is connected to a T1 stratum referenceclock source 1736 or another clock source commonly used for various N×64and/or N×56 digital telephone company services that may involveplesiochronous digital hierarchy (PDH) or synchronous digital hierarchy(SDH) multiplexing. On the TMTS-side, T1 stratum reference clock source1736 (or another clock source as would be known by someone of ordinaryskill in the art) generally is an input to IMS 1308 in a TMTS. Incontrast on the cTM-side, T1 stratum reference clock source 1736 (oranother clock source as would be known by someone of ordinary skill inthe art) generally is an output that is driven by the IMS 1308 in a cTM.

The preferred embodiments of the present invention generally involveproviding a frequency-division multiple access (FDMA) architecture totransparently carry frames of data between customer premises equipmentand service provider equipment. The preferred embodiments of the presentinvention will function over not only hybrid fiber-coax systems but alsoover all fiber systems. Furthermore, the preferred embodiments of thepresent invention will work over cable distribution networks in asub-split configuration that may be carrying legacy CATV video channels.Additionally, the preferred embodiments will work over bandwidth-splitconfigurations.

In the downstream direction the preferred embodiments of the presentinvention support a point-to-multi-point configuration where a single 6MHz channel provides one direction of traffic flow for one or morecustomer premises devices known as client transport modems (cTM).Downstream traffic in a 6 MHz channel may be shared by more than one cTMwith each cTM being allocated a certain number of bits from thedownstream modulators. To provide synchronization that allows a cTM toproperly select the correct downstream bits and ignore the downstreambits destined for other cTMs, a framing method is used.

The MPEG 2 (Moving Picture Experts Group) transport stream is onenon-limiting way of handling this framing functionality. Advantageously,MPEG 2 transport already is commonly used in CATV networks to deliverdigital video and audio. Furthermore, MPEG 2 transport already includessynchronization mechanisms that can be used to align the clocks of cTMs.Also, MPEG 2 transport is a multiplexing mechanism that allows the highspeed data of the preferred embodiments of the present invention to bepotentially multiplexed with other MPEG 2 data in CATV networks.

In the upstream direction the standard 6 MHz channels of RF cablenetworks may be subdivided into multiple tones to allow frequencyallocations to be managed at a much smaller granularity. Each one ofthese tones can be allocated to a different cTM. The preferredembodiments of the present invention avoid all the problems of DOCSIS inranging and contention resolution (or media access control) by limitingthe allocation of an upstream tone to one cTM at any particular time.Thus, the upstream direction generally represents a point-to-pointarchitecture with one cTM communicating with one server transport modem(sTM) function. A plurality of these server transport modems may beimplemented in a central-site concentrator known as a transport modemtermination system (TMTS).

As discussed above the preferred embodiments of the present inventiongenerally carry downstream information in MPEG packets. The MS sublayerof the TMTS is generally responsible for placing the downstreaminformation into MPEG packets while the MS sublayer of the cTM generallyis responsible for recovering the information from the MPEG packets.FIG. 22 generally shows the downstream behavior of the TMTS MS sublayer2202 and the cTM MS sublayer 2204. A plurality of 184 octet MPEG packetpayloads 2206 may be contemporaneously transmitted downstream. Each ofthe contemporaneously transmitted MPEG packets is carried on its owndownstream carrier frequency such as 2208. In the preferred embodimentof the present invention downstream carrier frequency such as 2208 is a6 MHz frequency channel that is commonly found in CATV networks.

TMTS IMS 2202 is shown with three downstream data flows 2214, 2216, and2218. Two of the downstream data flows 2214 and 2218 may be destined forone cTM IMS sublayer 2204. The other downstream data flow 2216 may bedestined for a cTM IMS sublayer in a different client transport modem.The downstream data flows 2214, 2216, and 2218 generally are framemanagement sublayer data flows and carry information in FMS frames 1602of FIG. 16. Downstream multiplexer in the TMTS 2222 is responsible forplacing the downstream data flows into the correct MPEG packets whiledownstream inverse multiplexer 2224 is responsible for recovering thedata flows from the correct MPEG packets.

FIG. 22 shows four MPEG packets 2232, 2242, 2252, and 2262 which eachhave an MPEG header 2234, 2244, 2254, and 2264 respectively. As shown inFIG. 22 octets from a single data flow are spread across a plurality ofcontemporaneously transmitted MPEG packets. For example, octets 2235,2237, 2258, and 2266 of data flow 1 are spread across MPEG packets 2232,2252, and 2262. Also, octets 2245, 2255, 2267, and 2268 of data flow 2are spread across MPEG packets 2242, 2252, and 2262. In addition, octets2238, 2246, 2247, and 2265 of data flow 3 are spread across MPEG packets2232, 2242, and 2262. Empty octets 2236, 2248, 2256, and 2257 of MPEGpackets 2232, 2242, and 2252 currently are not allocated to any dataflow. Because the FMS data flows continuously transmit octets with 0x7Ewhen there is no data to transmit, the octets of an MPEG packet that areallocated to a particular data flow generally contain either an octetfrom an FMS frame or the continuously transmitted 0x7E when there is nodata from an FMS frame to be transmitted on an FMS data flow. FIG. 23shows a more detailed diagram of the downstream functionality of a TMTSmultiplexer. An N port FMS sublayer 2302 communicates information toTMTS IMS downstream multiplexer 2304, which is further communicated todownstream PCS sublayer 2306 through various intermediate steps. N portFMS 2302 communicates information to write multiplexer 2312 which isresponsible for managing the placement of data into ethernet data framebuffer (EDFB) 2314. EDFB 2314 is related to the frame buffers in FIG.13. In general, N frame buffers may be implemented as a group of memorywith write multiplexer 2312 and control bus 2356 specifying the correctmemory address location associated with the proper FMS data flow. EDFB2314 has one or more ring buffers associated with each data flow. Thering buffers keep up with pointers that specify the beginning addressand ending address of valid data to be transferred to inversemultiplexer 2316. The behavior of inverse multiplexer 2316 will bedescribed in more detail with respect to FIG. 24. However, inversemultiplexer 2316 generally reads data from EDFB 2314 and places it intoone of P MPEG buffers shown as 2322 and 2324. Each MPEG buffer isassociated with an MPEG framer shown as 2332 and 2334. MPEG framers 2332and 2334 actually form MPEG frames including the MPEG headers andpotentially adaptation fields that carry the program clock referenceamong other items. In the preferred embodiment of the present inventioneach group of four MPEG streams is converted into one asynchronousinterface stream in P/4 ASI stream multiplexer 2336. These ASI streamshave physical interfaces 2342 and 2344. The ASI streams are furtherpassed to QAM modulators in PCS 2306. In other alternative embodimentsof the present invention the MPEG streams go directly to the QAMmodulators without utilizing ASI interfaces.

Furthermore, FIG. 23 also shows some of the hardware and/or softwarelogic used to control the downstream communication of information fromFMS sublayer 2302 into TMTS IMS downstream multiplexer 2304 and furtherinto downstream PCS 2306. Control buses 2355 and 2356 carry at leastsome of the signals that drive this downstream communication through thesublayers in FIG. 23. In general, the preferred embodiments of thepresent invention use software and/or hardware to implement variouslogical functions. One skilled in the art will be aware of thetrade-offs between implementing various functions in hardware, software,and/or some combination of hardware and software. Furthermore, oneskilled in the art will be aware of methods for communicating signalsbetween various portions of hardware and/or software. Also, one skilledin the art will be aware of the timing issues and techniques used ininterfacing different types of hardware, logic, and/or circuitry toother hardware, logic, and/or circuitry. Moreover, one skilled in theart will be aware that interface buses are commonly used to facilitatethe interconnection of hardware, logic, and/or circuitry. In addition,one skilled in the art will be aware that there are many other ways inaddition to buses to handle the interconnection of hardware components.Thus, the use of buses is only one non-limiting example of hardwareinterconnection that may be used in the preferred embodiments of thepresent invention. One skilled in the art will be aware of other typesof hardware interconnection as well as the various issues andcomplexities in utilizing various types of interconnections between andamong hardware, logic, and/or circuitry.

As described with respect to FIGS. 20 and 21, the preferred embodimentsof the present invention include a connection for a T1 reference clock2361, which is input into T1 physical layer interface 2362. FIG. 21 alsoshows how the T1 clock is related to MPEG program clock reference (PCR)2364. This PCR information is used in MPEG multiplexer/framer statemachine 2366 that generates the changing values in the MPEG headers andpasses the information to MPEG framers 2332 and 2334. Also, the TMTSincludes TMTS controller 2372 that operates with downstream map statemachine 2374 to cause the ethernet data from the correct data flow to beplaced in the proper octet of the MPEG frames. This downstream map statemachine 2374 also utilizes downstream map buffer 2376 which specifiesthe mapping of data flows into octets of MPEG packets.

FIG. 24 further shows the general behavior of downstream map statemachine 2374 and its interaction with ethernet data frame buffer 2314 tocause the correct octets to be placed into MPEG buffers 2322 and 2324.FIG. 24 shows a small portion of the ethernet data frame buffer(s)(EDFB) 2402 as well as a portion of the MPEG buffers 2404. Basically,the octets in EDFB 2402 are read and moved across data bus 2406 to bewritten into MPEG buffers 2404. Arrow 2407 shows the ethernet bufferread-out direction, while arrow 2408 shows the MPEG buffer write-indirection. Also, arrow 2409 shows the MPEG buffer read-out direction,which generally relates to the direction that octets are transmitted onthe cable distribution network. In FIG. 24 a non-limiting example of thepreferred embodiments of the present invention would contemporaneouslycommunicate octet No. 1 of MPEG buffer Nos. 1, 2, 3, and 4 on fourdifferent downstream 6 MHz channels. Also, in the non-limiting exampleof the preferred embodiments of the present invention, octet No. 2 ofMPEG buffer Nos. 1, 2, 3, and 4 in FIG. 24 generally would becontemporaneously communicated on four different downstream 6 MHzchannels. Similarly, in the non-limiting example of the preferredembodiments of the present invention, octet No. 3 of MPEG buffer Nos. 1,2, 3, and 4 in FIG. 24 generally would be contemporaneously communicatedon four different downstream 6 MHz channels. Furthermore, in thenon-limiting example of the preferred embodiments of the presentinvention, octet No. 4 of MPEG buffer Nos. 1, 2, 3, and 4 in FIG. 24generally would be contemporaneously communicated on four differentdownstream 6 MHz channels.

One skilled in the art will be aware that the concepts of the preferredembodiments of the present invention may transmit MPEG frames on atleast one downstream frequency channel, and the use of a plurality ofdownstream frequency channels instead of just one frequency channelgenerally allows contemporaneous transmission of multiple MPEG packetsand the corresponding octets. Thus, the choice of four MPEG buffers(Nos. 1, 2, 3, and 4) shown in FIG. 24 is only a non-limiting examplethat is used to better illustrate the possibility of utilizing more thanone downstream frequency channel in the preferred embodiments of thepresent invention. In general, the portion of EDFB 2402 shown in FIG. 24has five octets and buffers numbered 1 to E. One skilled in the art willbe aware that this is a small example of a communication systemutilizing the preferred embodiments of the present invention, and actualimplementations would have more than five octets in EDFB 2402 as well asmore than four octets in each of the four exemplary buffers of MPEGbuffer(s) 2404.

In general the octets of the EDFB 2402 are labeled in FIG. 24 with anordered pair of (EDFB buffer number—EDFB octet number). For example,octet 4 of buffer 3 in EDFB 2402 is (3-4). Also, the five octets of EDFB2402 buffer 1 are 2411, 2412, 2413, 2414, and 2415; the five octets ofEDFB 2402 buffer 2 are 2421, 2422, 2423, 2424, and 2425; the five octetsof EDFB 2402 buffer 3 are 2431, 2432, 2433, 2434, and 2435; the fiveoctets of EDFB 2402 buffer 4 are 2441, 2442, 2443, 2444, and 2445; andthe five octets of EDFB 2402 buffer E are 2451, 2452, 2453, 2454, and2455.

The values in these octets are read-out of EDFB 2402 according toethernet buffer read-out direction 2407 and moved into the four MPEGbuffer(s) 2404 according to the MPEG buffer write in direction 2408whenever the allocation MAP specifies the same octet number for two ormore MPEG buffers. (Because the data from the MPEG buffers 2404generally is transmitted contemporaneously downstream with each MPEGbuffer relating to an MPEG packet on its own carrier frequency, the No.1 octets of MPEG buffers No. 1 through 4 are transmittedcontemporaneously.) Also, the No. 2 octets of MPEG buffers No. 1 through4 are transmitted contemporaneously. Thus, MPEG buffer write-indirection 2408 is the sequence for filling the MPEG buffers when theallocation maps specify that one FMS data flow is to the same octetnumber in two or more contemporaneously transmitted MPEG packets.Furthermore, the data in the EDFB buffers 2404 from FMS data flowsgenerally is serial or sequential in nature with the value in octet 1 ofany one of the EDFB buffer numbers 1 through E preceding the value ofoctet 2 in the same EDFB buffer number. In addition, the transmission ofan MPEG packet that is formed based upon one of the MPEG buffers(numbered 1 through 4 in this example) is also sequential in nature suchthat the value in octet 1 of MPEG buffer 1 generally is transmitteddownstream before the value in octet 2 of MPEG buffer 1. Thus, ingeneral the information in an FMS data flow as held in one of thebuffers of EDFB 2404 is read out in FIG. 24 in a right-to-left fashion.This information is written into the MPEG buffer(s) 2404 first in atop-to-bottom fashion (according to arrow 2408 that shows the MPEGbuffer write-in direction) and then in a left-to-right fashion. Thevalues in MPEG buffers 2404 generally are read out in a left-to-rightfashion for downstream communication through a PCS sublayer and over acable transmission network. The information of each of the MPEG databuffer(s) 2404 that are numbered 1 to 4 are read out in parallel for allfour of the exemplary MPEG data buffers numbered 1 through four.

As an example, the values in octets 2431 (or 3-1), 2432 (or 3-2), and2433 (or 3-3) generally are sequential octets of an FMS data flowcomprising FMS data frames 1602 as shown in FIG. 16 that may be carryingethernet/802.3 data frames or control frames. The value of octet 2431(or 3-1) is read out of octet 1 of EDFB 2402 buffer No. 3 and writteninto octet 1 of MPEG buffer 2404 No. 1 prior to the value of octet 2432(or 3-2) being read out of octet 2 of EDFB 2402 buffer No. 3 and beingwritten into octet 1 of MPEG buffer 2404 No. 4. Furthermore, the valuein octet 2432 (or 3-2) is read out of octet 2 of EDFB 2402 buffer No. 3and written into octet 1 of MPEG buffer 2404 No. 4 prior to the value inoctet 2433 (or 3-3) being read out of octet 3 of EDFB 2402 buffer No. 3and being written into octet 4 of MPEG buffer 2404 No. 4. Then, thevalue of octet 2431 (or 3-1) is transmitted downstream contemporaneouslywith the value in octet 2432 (or 3-2), although the two octets arecarried in different MPEG packets that are transmitted in parallelacross multiple carrier frequencies. Also, the MPEG packet carrying theinformation from MPEG buffer 2404 No. 4 carries the values of the twoconsecutive or sequential octets 2432 (or 3-2) and 2433 (or 3-3) from anFMS data flow that was held in EDFB 2402 buffer No. 3. However, the MPEGpacket that is formed (based upon MPEG buffer 2404 No. 4) now hasintervening octets 2413 and 2414 (associated with different FMS dataflows) between octet 2432 (or 3-2) and octet 2433 (or 3-3).

The process of reading from the ethernet data frame buffer(s) (EDFB)2402, which generally contain FMS frames, and writing to MPEG buffer(s)2404 is at least partially driven by counter 2462. Because MPEG packetsare fixed length with 184 octets of payload, a counter 2462 can cyclethrough the octet positions of MPEG buffer(s) 2404, which generally holdfixed length MPEG payloads. The counter 2462 supplies its value as awrite address for MPEG buffer(s) 2404. Also, the counter 2462 suppliesits value as a read address 2466 to allocation map 2468, which generallykeeps track of the relationship specifying the location in MPEG packetswhere the octets of FMS data flows contained in EDFB 2404 are to beplaced. Allocation map 2468 may be implemented at least partially as amemory lookup table that uses read address 2466 to read out the valuefrom the memory look up table associated with allocation map 2468. Thevalue from the lookup table together with pointer control 2476information from write multiplexer 2474 provides the information neededto generate the read address(es) 2472 of the EDFB 2402. As describedwith respect to FIG. 23, the ethernet data frame buffer(s), which arelabeled as EDFB 2402 in FIG. 24, have one or more ring buffers with theposition in each of the ring buffer determined based on at least twopointers associated with each ring buffer. The two pointers for eachring buffer specify the next write location for writing octets of FMSframes into a ring buffer of EDFB 2402 and specify the next readlocation for reading octets of the FMS frames out of the ring buffer ofEDFB 2402 and into the MPEG buffer(s) 2404. Basically, the read andwrite pointers for each ring buffer keep track of which octets in EDFB2402 contain valid information from FMS frames and which octets in EDFB2402 have not yet been written to an MPEG payload as represented by theMPEG buffer(s) 2404.

It should be emphasized that the above-described embodiments of thepresent invention, particularly, any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of the principles of the invention. Many variations andmodifications may be made to the above-described embodiment(s) of theinvention without departing substantially from the spirit and principlesof the invention. All such modifications and variations are intended tobe included herein within the scope of this disclosure and the presentinvention and protected by the following claims.

MPEG Packets

FIG. 18 shows the layout of an MPEG frame that is known to one of skillin the art and is described in ITU-H.222.0 entitled “Audiovisual andMultimedia Systems” and ITU-T J.83 entitled “Transmission of Television,Sound Program and Other Multimedia Signals”, which are both incorporatedby reference in their entirety herein. Synchronization Byte (SB) 1812contains the eight bit value 0×47 hexadecimal. The transport errorindicator (TEI) 1822 is set in a communication system using thepreferred embodiments of the present invention to indicate framedecoding errors of MPEG packets to an 802.3 MII Interface connected to aframe management sublayer. The cable transmission physical layer(including the four sublayers of FMS, IMS, PCS, and SMD) in acommunication system utilizing the preferred embodiments of the presentinvention generally does not utilize payload start indicator (PSI) 1824,transport priority (TP) bit 1826, and the transport scrambling control(TSC) bits 1842.

The cable transmission physical (CT PHY) layer of a communication systemutilizing the preferred embodiments of the present invention doesutilize the thirteen bit packet identifier (PID) field to specifyvarious streams of MPEG packets. In general, the PID numbers 0×0000through 0×000F are not used to carry the cable transmission physical (CTPHY) layer communications in a system operating with the preferredembodiments of the present invention. These PIDs of 0×0000 through0×000F are utilized for other MPEG functions such as but not, limitedto, program association table (PAT), conditional access table (CAT), andtransport stream description table that are known to one of skill in theart. In addition, the preferred embodiments of the present invention donot utilize the PIDs of 0×1FFF, which indicates the null packet, and0×1FFE, which indicates DOCSIS downstream communications. PIDs in therange of 0×0010 through 0×1FFD are utilized to carry the cabletransmission physical layer (CT PHY) information in a communicationsystem using the preferred embodiments of the present invention. ThePIDs are allocated for carrying the information of FMS data flows bystarting at 0×1FFD and working downward.

The four bits of the continuity counter (CC) 1846 increment sequentiallyfor each packet that belongs to the same PID. The IMS downstreamcommunication of MPEG packets are generated contemporaneously inparallel with the same value for the continuity counter (CC) 1846 acrossall the parallel packets. The continuity counter 1846 is incremented inunison across all the MPEG stream to help ensure that inversemultiplexing operations across multiple MPEG streams are performedutilizing the correctly aligned set of packet payloads.

The two bits of the adaptation field control (AFC) 1844 specifieswhether the payload contains a packet payload only, an adaptation fieldonly, or a packet payload and an adaptation field. The 184 octets of anMPEG packet or frame after the four octet header may contain anadaptation field and/or a packet payload 1852, and is padded to thefixed size of 184 octets with pad 1854. In general, the preferredembodiments of the present invention do not generate MPEG packetscontaining both adaptation fields and other payload information.However, one skilled in the art will be aware that other implementationsare possible using various combinations of adaptation fields and payloadinformation in MPEG packets.

FIG. 19 further shows an MPEG adaptation field that has been slightlymodified from the standard MPEG adaptation field known to one ofordinary skill in the art. The cable transmission physical layer (CTPHY) of a communication system using the preferred embodiments of thepresent invention generally does not utilize the MPEG adaptation fieldbits of the discontinuity indicator (DI) 1921, the random accessindicator (RAI) 1922, the elementary stream priority indicator (ESPI)1923, the original program clock reference flag (OPCRF) 1925, the splicepoint flag (SPF) 1926, the transport private data flag (TPDF) 1927, andthe adaptation field extension flag (AFEF) 1928.

The adaptation field length 1912 comprises eight bits that specify thenumber of octets in an adaptation field after the adaptation fieldlength itself. In the preferred embodiments of the present invention, ifan MPEG packet includes an adaptation field, the adaptation field length(AFL) 1912 may range from 0 to 182 octets (with the count starting atthe first octet after the AFL octet 1912). The MPEG packets generated bythe preferred embodiments of the present invention that carry anadaptation field generally have the program clock reference flag (PCRF)set to 1 to indicate that a program clock reference is carried in theadaptation field. The thirty-three bit program clock reference (PCR)1932 and the nine bit program clock reference extension (PCRE) 1982 areconcatenated into a forty-two bit counter with the PCRE being the leastsignificant bits of the counter. The forty-two bit counter generally isused to indicate the intended time of arrival of the octet containingthe last bit of the program clock reference (PCR) at the input to aninverse multiplex sublayer (IMS) of a client transport modem (cTM).Also, the reserved bits 1972 are not utilized in the preferredembodiments of the present invention.

The maintenance channel PID (MC PID) 1992 is used to allow a clienttransport modem (cTM) to startup and establish communications with atransport modem termination system (TMTS) to begin a registrationprocess. Initially, the cTM listens to at least one low bandwidthmaintenance channel established by the TMTS. The TMTS continuouslybroadcasts maintenance-oriented information on at least one lowbandwidth maintenance channel that is specified by at least one MC PID1992. The maintenance information includes multiplexing maps as well asother registration information. The client transport modem determinesthe maintenance channel PID 1992 by listening to downstream MPEG packetscontaining the adaptation field. Based on the value of the MC PID 1992,the client transport modem will know which downstream MPEG packetscontain maintenance channel information. Furthermore, the maintenancechannel map (MC-MAP) 1994 comprises twenty-three octets or23.times.8=184 bits that specify the octets in the downstream MPEGpackets with a PID equal to MC-PID 1992. Each bit in the MC-MAPrepresents one octet in the 184 octet MPEG payload of the MPEG packetswith a PID value equal to MC-PID. This map of bits (MC-MAP) and the PIDvalue (MC-PID) allow a client transport modem to select and inversemultiplex through the IMS sublayer the information of the low bandwidthdownstream maintenance channel.

Network Clocking

Although most of the description of the preferred embodiments of thepresent invention has related to communication of ethernet/802.3 framesbetween cable transmission physical (CT PHY) layer peer entities, thepreferred embodiments of the present invention also allow communicationof circuit emulation services (CES) that generally are associated withthe N.times.56 and N.times.64 interfaces of telephone company serviceproviders. Despite the increasing deployment of packetized voiceconnectivity, many communication systems still utilize these variousN.times.56 and N.times.64 services and will continue to do so for theforeseeable future. Thus, offering a T1 or other type of N.times.56/64interface allows customers to easily connect their existing voicenetworking equipment to a client transport modem. This allows thepreferred embodiments of the present invention to support remote officeswith packetized sevice of ethernet for data as well as circuit emulationsevice for legacy voice applications.

However, most customer oriented N.times.56 and N.times.64 equipment suchas, but not limited to, a PBX (private branch exchange) with a T1interface usually expects the T1 line from the service provider tosupply the necessary network clocking. To be able to replace current T1services of a customer, the preferred embodiments of the presentinvention generally should also be able to supply the necessary networkclocking to customer premises equipment (CPE) such as a PBX. Becausemore accurate clocks such as atomic clocks are more expensive, the moreexpensive central office and/or service provider equipment (such as acentral office switch or exchange) generally has a more accurate clockthan the less expensive customer premises equipment (such as a privatebranch exchange). Thus, equipment primarily designed for use at acomputer premises as opposed to in a sevice provider network generallyis designed to use the clock derived from the clock delivered overservice provider transmission lines or loops. One skilled in the artwill be aware that these network clocking issues apply to all networkingequipment and not just the limited example of PBXs and central officeswitches. These clocking issues for 8 kHz clocks are particularlyrelevant for equipment designed to utilize N.times.56/64 services (i.e.,services based on multiples of a DS0).

FIG. 20 shows a way of delivering the proper clocking to customerpremises equipment using a transport modem termination system and aclient transport modem. Dashed line 2002 generally divides FIG. 20between TMTS 2004 and cTM 2006. Both TMTS 2004 and cTM 2006 areconnected into cable transmission network 2008. Furthermore, TMTS 2004comprises various potential clock inputs including, but not limited to,downstream T1 input 2012, 8 kHz input clock 2014, as well as 27 MHz MPEGinput clock 2016. These clock inputs are expected to be commonly foundin the headend and/or distribution hub of cable sevice providers.

Generally, the 8 kHz clock 2014 is related to the N.times.56 kbps andN.times.64 kbps services. 8 kHz is the Nyquist sampling rate to be ableto properly sample a 0 to 4 kHz analog POTS (Plain Old TelephoneService) voice frequency channel. With each sample having eight bits (orone octet), eight bits transmitted at 8 kHz (or 8000 cycles per second)yields a 8.times.8000=64,000 bits per second or 64 kbps. Many higherorder PDH and SDH multiplexing techniques are based on multiples of thisDS0 speed of 64 kbps or 56 kbps. Thus, an 8 kHz clock with a 1/8 kHz or125 microsecond period is commonly available at N.times.56/64 interfacesto the public switched telephone network (PSTN).

Downstream T1 input 2012 generally also has a corresponding upstream T1clock and data 2018 because T1 services are bi-directional. However, theservice provider (or in this case downstream) clock generally isconsidered to be the master reference. Customer equipment clockinggenerally is derived from reference clocking of service provider ordownstream services. As further shown in FIG. 20, the downstream T1input 2012 and upstream T1 clock and data 2018 generally are connectedin the TMTS to a T1 physical layer and framer (2022). One skilled in theart will be aware of various issues in T1 framing including variousframing issues such as extended superframe (ESF) and D4 framing,synchronization based on the 193rd bit, as well as various physicallayer technologies such as, but not limited to, alternate mark inversion(AMI) and 2B 1Q of HDSL (High bit rate Digital Subscriber Line) forcarrying the 1.536 Mbps (or 1.544 Mbps) T1 service. In addition, thoughthe preferred embodiments of the present invention generally aredescribed with respect to North American T1 service, EuropeanN.times.56/64 services such as E1 also could be used. The output of T1physical (PHY) layer interface and framer 2022 comprises an 8 kHz clocksource.

-   -   In addition, because a TMTS using the preferred embodiments of        the present invention generally is expected to be often deployed        at cable headends and/or distribution hubs, a 27 MHz MPEG input        clock 2016 is expected to be available based on the ubiquitous        deployment of MPEG in digital cable television (CATV) networks.        An 8 kHz reference clock may be derived from the 27 MHz clock by        dividing by 3375 at item 2024. The 27 MHz MPEG clock, which        generally is used for digital movies, turns out to be an exact        multiple of 3375 times the 8 kHz clock, which generally is used        for N.times.56/64 services associated with the PSTN. The three        input clocks from MPEG, T1, and an 8 kHz reference are converted        to 8 kHz clocks. Reference clock selection 2026 may be a switch        that selects among the various 8 kHz reference clocks. As would        be known by one of skill in the art, this clock selection        switching could be implemented by mechanisms such as, but not        limited to, software controlled switches, manual physical        switches, and/or jumpers.

The selected 8 kHz clock reference is then input into phase locked loop(PLL) 2030, which further comprises phase detector 2032, loop filter2034, a 162 MHz voltage controlled crystal oscillator (VCXO) of TMTSmaster clock 2036. The 162 MHz output of TMTS master clock 2036 isdivided by 20,250 at item 2038 and fed back into phase detector 2032. Asa result, phase locked loop (PLL) provides a loop that is used forlocking the relative phases of the 8 kHz clock relative to the 162 MHzTMTS master clock 2036. Phase locked loops are known to one of skill inthe art.

The 162 MHz master clock 2036 is divided by 6 at item 2040 to generate a27 MHz clock before being input into a 42-bit counter and MPEG framer2046 that performs the function of inserting the program clock referenceinto MPEG frames. Interval counter 2042 generates a 0.1 Hz intervalclock 2044 that generally determines that rate at which snapshots of the42 bit counter are sent downstreams as the program clock reference (PCR)in the adaptation field of MPEG packets. The MPEG frames arecommunicated downstream to client transport modem 2006 using QAMmodulator(s) 2048, which may be integrated into TMTS 2004 or could beexternal to TMTS 2004.

On the downstream side the client transport modem (cTM) 2006 includesthe hardware and/or software to properly extract the MPEG frames andinterpret the fields. These functions might be performed in cTMdownstream front end to extract MPEG 2052 and program clock referenceparser 2054. Based on the PCR value extracted from MPEG adaptationfields, the client transport modem 2006 determines how much the cTMmaster clock has drifted relative to the TMTS master clock. Counter andloop control 2062 determines the amount and direction of the relativeclock drifts between the cTM and the TMTS and sends control signals tothe cTM oscillator to correct the relative clock drift. Thus, thecounter and loop control 2062 regulates the cTM clock to ensure theproper relationship relative the TMTS master clock 2036.

In the preferred embodiment of the present invention, the cTM utilizes a162 MHz voltage controlled crystal oscillator (VCXO) 2064 that operatesbased on a 162 MHz crystal (XTAL) 2066. The 162 MHz clock is divided by6 at item 2068 to result in a 27 MHz clock that is the cTM master clock2072. This 27 MHz cTM master clock has been generally locked to the TMTSmaster clock 2036, which was further locked to the 8 kHz referencesource in phase locked loop (2030) of TMTS 2004. After dividing the 27MHz cTM master clock 2072 by 3375 in item 2074, an 8 kHz clock isrecovered that generally is locked to the 8 kHz reference clocks of TMTS2004. As a result the 8 kHz clock of cTM 2006 generally can be usedsimilarly to a service provider master clock for N.times.56/64 servicessuch as, but not limited to, T1. The 8 kHz clock is an input into T1physical layer interface and framer 2076 which provide downstream T1output 2082 that can be used as a network service provider clock byother CPE (such as but not limited to a PBX). In addition, the upstreamT1 clock and data from CPE such as, but not limited to a PBX, providesthe bi-directional communication generally associated with T1. However,the clock associated with upstream T1 clock and data 2088 from a PBX orother CPE generally is not a master clock, but a derived clock based onthe downstream T1 output 2082, that is based on the master clock of aservice provider.

In general, the downstream delivery of MPEG packets with PCR informationis used as a network clock distribution mechanism to clock transfers ofinformation in the opposite direction to distribution of the clock.Normally, MPEG PCR information in downstream MPEG packets is used toclock downstream flows of audio/visual information. However, in thepreferred embodiments of the present invention, the downstream deliveryof MPEG PCR clock information is used to provide a stratum clock to lockthe upstream transmissions of circuit emulation services (CES) orN.times.56/N.times.64 services to the downstream network clock normallyprovided by service providers. Also, in the preferred embodiments of thepresent invention, the downstream distribution of MPEG packet containingPCR information is used to synchronize the upstream transmissions overmultiple tones from a plurality of cTMs to a TMTS. Thus, the PCRinformation contained in MPEG packets is used to provide networkclocking for communication that is in the opposite direction from thedirection that MPEG packets are propagated.

FIG. 21 shows a timing diagram of delivering an 8 kHz clock from a TMTSto a cTM using MPEG packets carrying program clock references (PCR). Thetiming diagram includes an 8 kHz reference clock 2102 that generally isassociated with N.times.56/64 kbps services. An 8 kHz reference clock2102 has a 125 microsecond period 2104. Normally, MPEG has a 27 MHzclock 2112 that has a period 2122 of approximately 37.037 nanoseconds.In general, the 8 kHz reference clock 2102 and the 27 MHz referenceclock 2112 will have an arbitrary relative phase difference 2106.However, the relative phase difference 2106 between the 8 kHz clock 2102and the 27 MHz clock 2114 is not significant so long as the clocks canbe controlled so that they do not significantly drift relative to eachother. In 6 MHz cable transmission frequency channels, MPEG packets maybe transmitted at 38 Mbps. Given a 188 octet fixed length MPEG packet,this packet can be transmitted in approximately (188 octets.times.8bits/octet)/38 Mbps=39.6 microseconds as illustrated at item 2124. A 27MHz MPEG clock generally will complete approximately 1069 clock ticks inthe 39.6 microseconds needed to transmit an MPEG packet of 188 octets at38 Mbps on a 6 MHz frequency channel ((188 octets X 8 bits/octet)/38Mbps)/( 1/27 MHz clock rate)). Moreover, two 188 octet MPEG packets canbe transmitted in 2.times.1069=2138 clock ticks of a 27 MHz clock; three188 octet MPEG packets can be transmitted in 3.times.1069=3207 clockticks of a 27 MHz clock; and four 188 octet MPEG packets can betransmitted in 4.times.1069=4276 clock ticks of a 27 MHz clock. Also, 27MHz/8 kHz=3375 clock ticks of the MPEG 27 MHz clock 2112 occur in oneclock tick of an 8 kHz clock 2102 with a 125 microsecond period 2104.The 8 kHz clock 2102 has a transition in 125 microseconds/2=62.5microseconds, which is associated with 3375/2=1687 clock ticks of the 27MHz MPEG clock 2112. These relevant clock counts are shown in FIG. 21 as27 MHz TMTS clock counter values 2114.

The four MPEG packets (or MPEG transport stream (TS)packets) shown inFIG. 21 are labeled as 2132, 2134, 2136, and 2128. Although all the MPEGpackets have headers (HDR) only some of the MPEG packets (namely MPEGpacket 2132 and the MPEG packet following MPEG packet 2138) containprogram clock reference (PCR) values. The time distance between MPEGpackets containing PCR values generally is arbitrary as shown at item2142. However, the preferred embodiments of the present inventiongenerally should send PCR update values often enough to keep the TMTSand cTM clocks aligned to the desired level of accuracy. Item 2144 inFIG. 21 shows the counter values that are recovered from the MPEG PCRinformation received at a client transport modem (cTM). Because some ofthe MPEG packets received by a cTM generally will not contain PCR values(e.g., MPEG packets 2134, 2136, and 2138), a cTM generally will notrecover a clock counter value from those MPEG packets.

As shown in FIG. 21, MPEG PCR values 2144 can be used in the clienttransport modem (cTM) to compare and adjust the client transport modemclock 2152 using a voltage controlled crystal oscillator (VCXO) to keepit in sync with the transport modem termination system (TMTS) clock2112. Basically, the counter values recovered from the PCR 2144 arecompared with client transport modem (cTM) counter values 2154 to allowadjustment of the cTM clock 2152. The 27 MHz client transport modem(cTM) clock 2152 can then be used to generate a recovered 8 kHz stratumclock 2162 by dividing by 3375. In general, the recovered 8 kHz clock2162 at a cTM will have the same frequency as the 8 kHz reference clock2102 at the TMTS. However, because the TMTS clock counter 2114 may startat an arbitrary phase difference 2106 from a reference 8 kHz clock 2102at the TMTS, the 8 kHz clock 2162 recovered at a cTM will have anarbitrary (but generally fixed) phase difference 2106 from the 8 kHzreference clock 2102 at a TMTS.

Furthermore, because the MPEG packets carrying PCR values are deliveredto one or more cTMs and because the propagation delay on the cabledistribution network may be different to each cTM, the 8 kHz clock 2162recovered at any cTM generally will have an arbitrary (but basicallyfixed) phase difference 2106 from the 8 kHz reference clock 2102 of theTMTS and an arbitrary (but basically fixed) phase difference 2106 fromeach of the other 8 kHz recovered clocks 2162 at the other cTMs.Although the recovered 8 kHz clock 2162 at a cTM will have an arbitraryphase difference 2106 from the 8 kHz input reference clock 2102 of theTMTS, this clock phase difference 2106 is not a problem. Generally, thephase of a reference clock at a telephone company central office ifdifferent from the phase of the clock delivered to customer premisesequipment due at least to the propagation delays in the transmissionlines between the service provider and the customer premises. However,it generally is important to synchronize the frequency of the serviceprovider clock and the customer premises clocks so that the clocks donot significantly drift relative to each other. The recovered 8 kHzclock 2162 at the cTM is frequency-locked to the 8 kHz reference stratumclock 2102 at the TMTS (i.e., the clocks do not significantly driftrelative to each other).

By frequency-locking each cTM clock to the TMTS clock, frequencystability of the poorly regulated cTM clocks is ensured. In addition,the multi-tone upstream frequency division multiplexing receiver in theTMTS generally performs optimally when the frequency error of thetransmissions of different cTMs is small. Significant frequencydifferences in cTM clocks as well as the TMTS clock may create problemsin selecting the correct carrier frequency of the upstream multi-tonefrequency-division multiplexing. Thus, the downstream delivery of PCRinformation allows a plurality of client transport modems to properlyset their respective oscillation clocks that are used in generating thefrequency carrier signals. In this way each cTM can ensure that it isaccurately transmitting in the right upstream frequency range for a toneinstead of slightly interfering with an adjacent tone.

1. A method of providing a host with local area network connectivity andaccess to other services in a cable transmission network, the methodcomprising: allocating data bandwidth in the cable transmission networkto support bi-directional communication between the host and a centralconcentrator; conveying at least one data flow between the host and thecentral concentrator over the allocated data bandwidth; and utilizingbandwidth not allocated to data communications in the cable transmissionnetwork to provide the host with at least one audio/visual service,wherein the allocating data bandwidth further comprises: providing atleast two first frequency channels for a first direction ofcommunication between the host and the central concentrator; andproviding at least one second frequency channel for second direction ofcommunication between the host and the central concentrator, the seconddirection of communication being in an opposite direction to the firstdirection of communication; and wherein the conveying at least one dataflow further comprises: communicating first direction frames in thefirst direction, the first direction frames being fragmented to allowcontemporaneous communication of portions first direction frames overthe at least two first frequency channels; and communicating seconddirection frames in the second direction, the second direction framescommunicated over the at least one second frequency channel.
 2. Themethod of claim 1, wherein the first direction frames and the seconddirection frames are ethernet/802.3 frames.
 3. A method of providing aclient with local area network connectivity and access to other servicesin a cable transmission network, the method comprising: allocatingbandwidth in the cable transmission network to support bi-directionaldata communication between the host and a central concentrator;conveying a bi-directional data flow between the host and the centralconcentrator over the allocated bandwidth; and utilizing bandwidth inthe cable transmission network not allocated to data communications toprovide the host with at least one audio/visual service, wherein thebi-directional data flow includes a downstream data flow and an upstreamdata flow and the allocating bandwidth further comprises: allocatingbandwidth for the downstream data flow on at least one downstreamfrequency channel based on a mapping between the downstream data flowand a particular octet in a downstream packet; and allocating bandwidthfor the upstream data flow on at least one non-shared upstream tone; andwherein the conveying further comprises: conveying the upstream dataflow using the allocated bandwidth for the upstream data flow; andconveying the downstream data flow using the allocated bandwidth for thedownstream data flow.
 4. The method of claim 3, wherein the at least oneaudio/visual service is a cable television service.
 5. The method ofclaim 3, wherein the method is performed in a network interface card(NIC) of the client.
 6. The method of claim 3, wherein the at least onedownstream frequency channel is a plurality of downstream frequencychannels.
 7. The method of claim 3, wherein the at least one firstnon-shared upstream frequency channel is a plurality of upstreamfrequency channels.
 8. The method of claim 3, wherein the first upstreambandwidth and the first downstream bandwidth provide symmetric bandwidthbi-directional communications.
 9. The method of claim 3, wherein thefirst upstream bandwidth and the first downstream bandwidth provideasymmetric bandwidth bi-directional communications.
 10. The method ofclaim 3, wherein first upstream bandwidth and the first downstreambandwidth provide a connection-oriented service to the bi-directionalcommunications between the first device and the second device.
 11. Themethod of claim 3, wherein the first upstream bandwidth and the secondupstream bandwidth provide physical layer connectivity between the firstdevice and the second device.
 12. The method of claim 3, wherein the atleast one downstream frequency channel and the at least one non-sharedupstream frequency channel utilize a different amount of frequencybandwidth.
 13. The method of claim 3, wherein bi-directionalcommunication between the first device and the second devicecommunicates ethernet/802.3 frames.
 14. The method of claim 3, whereinbi-directional communication between the first device and the seconddevice communicates circuit emulation services.
 15. The method of claim3, wherein the downstream packet is an MPEG packet.
 16. A method ofproviding a client with local area network connectivity and access toother services in a cable transmission network, the method comprising:allocating bandwidth in the cable transmission network to supportbi-directional data communication between the client and a centralconcentrator; conveying a bi-directional data flow between the clientand the central concentrator using the allocated data bandwidth; andproviding the client with at least one audio/visual service usingbandwidth not allocated to the data flow, wherein the bi-directionaldata flow includes a downstream data flow and an upstream data flow andthe allocating bandwidth further comprises: allocating bandwidth for thedownstream data flow by providing a mapping between the downstream dataflow and a particular octet in a downstream packet; and allocatingbandwidth for the upstream data flow on a non-shared upstream tone; andwherein the conveying at least one data flow further comprises:conveying the upstream data flow using the allocated bandwidth for theupstream data flow; and conveying the downstream data flow using theallocated bandwidth for the downstream data flow.
 17. The method ofclaim 16, wherein the at least one audio/visual service is a cabletelevision service.
 18. The method of claim 16, wherein the method isperformed in a network interface card (NIC) of the client.
 19. Themethod of claim 16, wherein the at least one downstream frequencychannel is a plurality of downstream frequency channels.
 20. The methodof claim 16, wherein the at least one first non-shared upstreamfrequency channel is a plurality of upstream frequency channels.
 21. Themethod of claim 16, wherein the first upstream bandwidth and the firstdownstream bandwidth provide symmetric bandwidth bi-directionalcommunications.
 22. The method of claim 16, wherein the first upstreambandwidth and the first downstream bandwidth provide asymmetricbandwidth bi-directional communications.
 23. The method of claim 16,wherein first upstream bandwidth and the first downstream bandwidthprovide a connection-oriented service to the bi-directionalcommunications between the first device and the second device.
 24. Themethod of claim 16, wherein the first upstream bandwidth and the secondupstream bandwidth provide physical layer connectivity between the firstdevice and the second device.
 25. The method of claim 16, wherein the atleast one downstream frequency channel and the at least one non-sharedupstream frequency channel utilize a different amount of frequencybandwidth.
 26. The method of claim 16, wherein bi-directionalcommunication between the first device and the second devicecommunicates ethernet/802.3 frames.
 27. The method of claim 16, whereinbi-directional communication between the first device and the seconddevice communicates circuit emulation services.
 28. The method of claim16, wherein the downstream packet is an MPEG packet.